Method for operating an electric turning machine operatively connected to an internal combustion engine

ABSTRACT

A method for operating an electric turning machine (ETM) operatively connected to an internal combustion engine (ICE) are disclosed. An engine control unit (ECU) controls the ETM to operate as a motor with a first control strategy and as a generator with a second control strategy. The second control strategy is distinct from the first control strategy. The ECU controls switching the operation of the ETM from the first control strategy to the second control strategy when a sensor senses that a rotational speed of the ICE is equal to or above a minimum revolution threshold.

CROSS-REFERENCE

The present application is a continuation of U.S. patent applicationSer. No. 15/775,616 filed on May 11, 2018, which is a national entry ofInternational Patent Application No. PCT/IB16/56824 filed on Nov. 11,2016, which claims priority to U.S. Provisional Patent Application No.62/254,421, filed Nov. 12, 2015, the entirety of each of which isincorporated herein by reference.

FIELD OF TECHNOLOGY

The present technology relates to a method and system for operating anelectric turning machine operatively connected to an internal combustionengine.

BACKGROUND

In order to start the internal combustion engine of small vehicles, suchas a snowmobile, a recoil starter is sometimes provided. To start theengine, the user pulls on a rope of the recoil starter which causes thecrankshaft of the engine to turn. If the crankshaft turns fast enough,the engine can be started. If not, the rope needs to be pulled againuntil the engine starts.

In order to facilitate the starting of the engine, some vehicles havebeen provided with an electric starting system. This system consists ofan electric motor, known as a starter, which engages and turns a ringgear connected to the crankshaft via a Bendix™ mechanism, when anignition key is turned or a start button is pushed by the user. Thestarter turns the crankshaft fast enough to permit the starting of theengine, and once the engine has started, disengages the ring gear and isturned off. The vehicle has a battery to supply electric current to thestarter in order to turn the crankshaft.

Although it is very convenient for the user, electric starting systemsof the type described above have some drawbacks. The battery, thestarter and their associated components add weight to the vehicle. Aswould be understood, additional weight reduces the fuel efficiency ofthe vehicle and can affect handling of the vehicle. In the case ofsnowmobiles, this weight also makes it more difficult for the snowmobileto ride on top of snow. These electric starting systems also requireadditional assembly steps when manufacturing the vehicle and take uproom inside the vehicle.

To recharge the battery and to provide the electric current necessary tooperate the various components of the vehicle once the engine hasstarted, an electrical generator is operatively connected to thecrankshaft of the engine. As the crankshaft turns the rotor of theelectrical generator, the generator generates electricity.

In recent years, some vehicles have been provided with motor-generatorunits, also called starter-generators, which replace the starter and theelectrical generator. The motor-generator is operatively connected tothe crankshaft in a manner similar to the aforementioned electricalgenerator. The motor-generator unit can be used as a starter or as agenerator. By applying current to the motor-generator unit, themotor-generator unit operates as a starter and turns the crankshaft toenable starting of the engine. When the motor-generator is operated as agenerator, the rotation of the crankshaft causes the motor-generator togenerate electricity. As would be understood, the use of such systemsaddresses some of the deficiencies of starting systems using separatestarters and electrical generators.

In order to start the engine, the torque applied to the crankshaft tomake it turn has to be sufficiently large to overcome the compressioninside the engine's cylinders resulting from the pistons moving up intheir respective cylinders as the crankshaft rotates. In order toprovide this amount of torque, the motor-generator unit needs to besufficiently large to properly operate as a starter.

Another problem relates to the control of the motor-generator. Whenoperating as a starter, the motor-generator generally operates at lowrotational speeds, sufficient to allow the onset of ignition in theinternal combustion engine. This operation requires the provision of acertain voltage to the motor-generator by the electric starting system.When operating as a generator, the motor-generator provides electricpower over a wide range of rotational speeds of the internal combustionengine, oftentimes far exceeding the starting rotational speed. Withoutspecific voltage control solutions, the motor-generator operating athigh rotational speeds could generate voltages that far exceed the needsof the various components of the vehicle.

There is therefore a need for a method and system for starting aninternal combustion engine that address at least some of the aboveinconveniences.

SUMMARY

It is an object of the present technology to ameliorate at least some ofthe inconveniences present in the prior art.

The present technology provides a system supporting an electrical startprocedure for an internal combustion engine (ICE) and a method forelectrical starting the ICE that uses an electric turning machine (ETM)connected to the crankshaft to start the engine. The method permits anelectrical start of the engine using a power source that is smaller andlighter than conventional batteries. In order to start the engine,electrical power is delivered from the power source to the ETM in afirst control strategy to rotate the crankshaft so that fuel injectionand ignition can occur. Once the engine is running, whether it has beenstarted manually by pulling the rope of a recoil starter or using theelectrical start procedure, electrical power is delivered from the ETMto an accessory in a second control strategy. For example, the accessorymay consist of the power source that may be recharged in view of afuture electrical start command. The electrical start procedure can bemade to conditional to an initial voltage of the power source beingequal to or above a minimum threshold. The first control strategy istailored to provide sufficient torque to rotate the crankshaft withoutfully depleting the energy stored in the power source. The secondcontrol strategy is tailored so that electrical power is delivered tothe accessory, for example to the power source, at a voltage thatremains fairly constant for a wide range of rotational speeds of thecrankshaft.

The present technology also provides a method for starting an internalcombustion engine (ICE) having a crankshaft. The method involves a coldstart of the ICE, followed by stopping of the ICE and then by restartingof the ICE using an electric start procedure. The ICE is cold-startedusing a recoil starter. While the ICE is running, an electric turningmachine (ETM) mounted to the crankshaft operates as a generator tocharge a power source that is smaller and lighter than conventionalbatteries. After stopping the ICE, the electric start procedure uses thepower source to deliver electrical power to the ETM, which is nowoperating as a starter.

The present technology further provides a method and a system for anassisted start of the ICE. When the crankshaft is rotated by use of therecoil starter, electric power is delivered from the power source to theETM to assist starting of the ICE. While the ICE is running, whether ithas been started manually by pulling the rope of a recoil starter, usingthe assisted start procedure to facilitate the task of pulling the ropeof the recoil starter, or using the electric start procedure, electricalpower is also delivered from the ETM to an accessory. The electric startprocedure and the assisted start procedure can be made conditional to aninitial voltage of the power source being equal to or above a minimumthreshold. The electric start procedure and the assisted start procedureare tailored to provide sufficient torque to rotate the crankshaftwithout fully depleting the energy stored in the power source. Someimplementations may include either the electrical start procedure or theassisted start procedure. Other implementations may include both theelectrical start procedure and the assisted start procedure.

According to a first aspect of the present technology, there is provideda method for operating an electric turning machine (ETM) operativelyconnected to an internal combustion engine. The method comprisesoperating the ETM as a motor with a first control strategy, operatingthe ETM as a generator with a second control strategy, the secondcontrol strategy being distinct from the first control strategy; andswitching from the first control strategy to the second control strategywhen a rotational speed of the internal combustion engine is equal to orabove a minimum revolution threshold.

In some implementations of the present technology, the method furthercomprises switching from the first control strategy to the secondcontrol strategy when a voltage of the ETM is equal to or above avoltage generation threshold.

In some implementations of the present technology, the method furthercomprises switching from the first control strategy to the secondcontrol strategy when the ETM has been operating with the first controlstrategy for at least a minimum time duration.

In some implementations of the present technology, the method furthercomprises operating the ETM as a generator in the first control strategybefore switching from the first control strategy to the second controlstrategy.

In some implementations of the present technology, the ETM operates as astarter for the internal combustion engine while controlling the ETMwith the first control strategy.

In some implementations of the present technology, pulse-widthmodulation (PWM) is used to control an electrical converter connectedbetween the ETM and a power source, the first control strategy includingfirst calculations to determine first widths and first timings of pulsesdelivered to the electrical converter, the second control strategyincluding second calculations different from the first calculations todetermine second widths and second timings of pulses delivered to theelectrical converter.

In some implementations of the present technology, the first controlstrategy comprises a vector control, the vector control comprisingcontrolling a delivery of electric power from a power source to the ETMbased on a pre-determined torque request sufficient to cause rotation ofthe internal combustion engine.

In some implementations of the present technology, the first controlstrategy comprises a vector control, the vector control comprisingdetermining a speed request sufficient to start the internal combustionengine, and controlling a delivery of electric power from a power sourceto the ETM based on the determined speed request.

In some implementations of the present technology, the method furthercomprises when the ETM is operating as a generator, shunting an outputof the ETM if the ETM generates a voltage that exceeds a maximum voltagethreshold.

In some implementations of the present technology, the method furthercomprises while operating with the first control strategy, deliveringelectric power from a power source to the ETM, and while operating withthe second control strategy, delivering electric power from the ETM toan accessory.

In some implementations of the present technology, when operating withthe second control strategy, the ETM delivers electric power to theaccessory at a desired voltage over a broad range of a rotational speedof the internal combustion engine.

In some implementations of the present technology, the power source isselected from a battery and a capacitance.

In some implementations of the present technology, the accessory is thepower source, the ETM operating as a generator to charge the powersource when being operating under the second control strategy.

In some implementations of the present technology, the method furthercomprises delivering electric power to the ETM using the first controlstrategy in response to sensing a command to start the internalcombustion engine.

In some implementations of the present technology, electric power isdelivered using the first control strategy if a voltage of the powersource is equal to or above a first minimum voltage threshold.

In some implementations of the present technology, the method furthercomprises terminating the delivery of electric power if the voltage ofthe power source falls below a second minimum voltage threshold lowerthan the first minimum voltage threshold.

In some implementations of the present technology, the method furthercomprises providing a manual start indication when terminating thedelivery of electric power.

In some implementations of the present technology, the first controlstrategy comprises delivering electric power from a power source to theETM, the method further comprising sensing a command to start theinternal combustion engine, and providing a manual start indication if avoltage of the power source is below a first minimum voltage threshold.

In some implementations of the present technology, the ETM is amulti-phase motor-generator, operating as a starter and as a generator.

In some implementations of the present technology, the method furthercomprises shunting one or more phases of the multi-phase motor-generatorwhen operating as a generator if the multi-phase motor-generatorgenerates a voltage that exceeds a maximum voltage threshold.

In some implementations of the present technology, the method furthercomprises regulating the voltage generated by the multi-phasemotor-generator in dissipative mode.

In some implementations of the present technology, the method furthercomprises regulating the voltage generated by the multi-phasemotor-generator in series mode.

In some implementations of the present technology, the internalcombustion engine comprises a cylinder, a cylinder head connected to thecylinder, a piston disposed in the cylinder, the cylinder, the cylinderhead and the piston defining a variable volume combustion chambertherebetween, and a crankshaft operatively connected to the piston,wherein the ETM is operatively connected to the crankshaft.

In some implementations of the present technology, the method furthercomprises delivering fuel in the combustion chamber as the piston movestoward its top dead center (TDC) position and igniting the fuel in thecombustion chamber as the piston moves beyond its TDC position.

In some implementations of the present technology, delivering the fuelin the combustion chamber comprises injecting the fuel in the combustionchamber.

According to a second aspect of the present technology, there isprovided a system for operating an electric turning machine (ETM)operatively connected to an internal combustion engine. The systemcomprises a sensor of a rotational speed of the internal combustionengine; and an engine control unit adapted for controlling an operationof the ETM as a motor with a first control strategy; controlling anoperation of the ETM as a generator with a second control strategy, thesecond control strategy being distinct from the first control strategy;and switching from the first control strategy to the second controlstrategy when the rotational speed of the internal combustion engine isequal to or above a minimum revolution threshold.

In some implementations of the present technology, the system furthercomprises a sensor of a voltage of the ETM, the sensor of the voltagebeing operatively connected to the engine control unit, wherein theengine control unit is adapted for switching from the first controlstrategy to the second control strategy when a voltage of the ETM isequal to or above a voltage generation threshold.

In some implementations of the present technology, the system furthercomprises a timer operatively connected to the engine control unit,wherein the engine control unit is adapted for using timing informationfrom the timer to switch from the first control strategy to the secondcontrol strategy when the ETM has been operating with the first controlstrategy for at least a minimum time duration.

In some implementations of the present technology, the engine controlunit is adapted for operating the ETM as a generator in the firstcontrol strategy before switching from the first control strategy to thesecond control strategy.

In some implementations of the present technology, the ETM operates as astarter for the internal combustion engine while controlling the ETMwith the first control strategy.

In some implementations of the present technology, the system furthercomprises a power source, and an electrical converter electricallyconnected to the ETM and to the power source, wherein the engine controlunit is adapted for using pulse-width modulation (PWM) to control theelectrical converter, the first control strategy including firstcalculations to determine first widths and first timings of pulsesdelivered to the electrical converter, the second control strategyincluding second calculations different from the first calculations todetermine second widths and second timings of pulses delivered to theelectrical converter.

In some implementations of the present technology, the first controlstrategy comprises a vector control, the vector control comprising acontrol by the engine control unit of a delivery of electric power froma power source to the ETM based on a pre-determined torque requestsufficient to cause rotation of the internal combustion engine.

In some implementations of the present technology, the first controlstrategy comprises a vector control, the vector control comprising adetermination by the engine control unit of a speed request sufficientto start the internal combustion engine, and a control by the enginecontrol unit of a delivery of electric power from a power source to theETM based on the determined speed request.

In some implementations of the present technology, the system furthercomprises an electrical converter electrically connected to an output ofthe ETM, and a sensor of a voltage at the output of the ETM, the sensorof the voltage being operatively connected to the engine control unit,wherein the engine control unit is adapted for causing the electricalconverter to shunt the output of the ETM when the ETM is operating as agenerator if the ETM generates a voltage that exceeds a maximum voltagethreshold.

In some implementations of the present technology, the system furthercomprises a crankshaft position sensor operatively connected to theengine control unit and adapted for detecting a mechanical position of acrankshaft of the internal combustion engine, wherein the engine controlunit is adapted for calculating an equivalent electrical angle of themotor-generator based on the mechanical position of the crankshaft andon a number of pole pairs of the motor-generator, initiating shuntingthe output of the ETM in synchrony with a voltage rise of themotor-generator.

In some implementations of the present technology, the engine controlunit is implemented on a single processor.

In some implementations of the present technology, the system furthercomprises an accessory and a power source electrically connected to theETM, wherein while operating with the first control strategy, the enginecontrol unit causes delivering electric power from the power source tothe ETM, and while operating with the second control strategy, theengine control unit causes delivering electric power from the ETM to theaccessory.

In some implementations of the present technology, the ETM is adaptedfor delivering electric power to the accessory at a desired voltage overa broad range of a rotational speed of the internal combustion enginewhen operating with the second control strategy.

In some implementations of the present technology, the power source isselected from a battery and a capacitance.

In some implementations of the present technology, the accessory is thepower source, the ETM operating as a generator to charge the powersource when being operating under the second control strategy.

1 In some implementations of the present technology, the system furthercomprises a sensor of a start command, wherein the sensor of the startcommand is operatively connected to the engine control unit, and theengine control unit is adapted for causing delivering electric power tothe ETM using the first control strategy in response to sensing acommand to start the internal combustion engine.

In some implementations of the present technology, the system furthercomprises a sensor of a voltage of the power source, wherein the sensorof the voltage of the power source is operatively connected to theengine control unit, and the engine control unit is adapted for causingelectric power being delivered using the first control strategy if avoltage of the power source is equal to or above a first minimum voltagethreshold.

In some implementations of the present technology, the system furthercomprises a display, wherein the display is operatively connected to theengine control unit, and the engine control unit is adapted for causingthe display to provide a manual start indication if the voltage of thepower source is below the first minimum voltage threshold.

In some implementations of the present technology, the engine controlunit is adapted for causing terminating the delivery of electric powerif the voltage of the power source falls below a second minimum voltagethreshold lower than the first minimum voltage threshold.

In some implementations of the present technology, the system furthercomprises a display, wherein the display is operatively connected to theengine control unit, and the engine control unit is adapted for causingthe display to provide a manual start indication when terminating thedelivery of electric power.

In some implementations of the present technology, the ETM is amulti-phase motor-generator, operating as a starter and as a generator.

In some implementations of the present technology, the system furthercomprises an inverter electrically connected to a multi-phase output ofthe multi-phase motor-generator, and a sensor of a voltage at themulti-phase output of the multi-phase motor-generator, the sensor of thevoltage being operatively connected to the engine control unit, whereinthe engine control unit is adapted for causing the inverter to shunt oneor more phases of the multi-phase motor-generator when operating as agenerator if the multi-phase motor-generator generates a voltage thatexceeds a maximum voltage threshold.

In some implementations of the present technology, the inverter isadapted for regulating the voltage generated by the multi-phasemotor-generator in dissipative mode.

In some implementations of the present technology, the inverter isadapted for regulating the voltage generated by the multi-phasemotor-generator in series mode.

In some implementations of the present technology, the internalcombustion engine comprises a cylinder, a cylinder head connected to thecylinder, a piston disposed in the cylinder, the cylinder, the cylinderhead and the piston defining a variable volume combustion chambertherebetween, and a crankshaft operatively connected to the piston,wherein the ETM is operatively connected to the crankshaft.

In some implementations of the present technology, the system furthercomprises a fuel delivery system operatively connected to the enginecontrol unit, and an ignition system operatively connected to the enginecontrol unit, wherein the engine control unit is adapted for causing thefuel delivery system to deliver fuel in the combustion chamber as thepiston moves toward its top dead center (TDC) position and to cause theignition system to ignite the fuel in the combustion chamber as thepiston moves beyond from its TDC position.

In some implementations of the present technology, fuel delivery systemfurther comprises a fuel injector adapted for injecting fuel in thecombustion chamber.

In some implementations of the present technology, fuel delivery systemfurther comprises an absolute position sensor operatively connected tothe engine control unit and adapted for detecting a mechanical positionof the crankshaft, wherein the engine control unit is adapted forcausing the fuel delivery system and the ignition system to respectivelyinject and ignite fuel in the combustion chamber according to themechanical position of the crankshaft.

According to a third aspect of the present technology, there is provideda method for operating an electric turning machine (ETM) operativelyconnected to an internal combustion engine. The method comprisesoperating the ETM as a motor with a first control strategy; andoperating the ETM as a generator with a second control strategy, thesecond control strategy being distinct from the first control strategy;switching from the first control strategy to the second control strategyoccurring when a rotational speed of the internal combustion engine isequal to or above a minimum revolution threshold; and switching the ETMfrom operating as a motor to operating as a generator occurring when therotational speed of the internal combustion engine is equal to or abovethe minimum revolution threshold.

Additional and/or alternative features, aspects and advantages ofimplementations of the present technology will become apparent from thefollowing description, the accompanying drawings and the appendedclaims.

BRIEF DESCRIPTION OF THE DRAWINGS

For a better understanding of the present technology, as well as otheraspects and further features thereof, reference is made to the followingdescription which is to be used in conjunction with the accompanyingdrawings, where:

FIG. 1 is a right side perspective view of a snowmobile;

FIG. 2 is a perspective view taken from a front, left side of theinternal combustion engine of the snowmobile of FIG. 1;

FIG. 3 is a rear elevation view of the engine of FIG. 2;

FIG. 4 is a cross-sectional view of the engine of FIG. 2 taken throughline 4-4 of FIG. 3;

FIG. 5 is a cross-sectional view of the engine of FIG. 2 taken throughline 5-5 of FIG. 4 with a drive pulley of a CVT mounted on a crankshaftof the engine;

FIG. 6 is a schematic diagram of components of a control system of theengine of FIG. 2;

FIG. 7 is a block diagram of a dual-strategy control system for deliveryof electric power between the capacitance and the electric turningmachine (ETM) of FIG. 6;

FIG. 8 is a block diagram of an energy management circuit for thecapacitance of FIG. 6;

FIG. 9 is a logic diagram of a method for starting the engine of FIG. 2according to an implementation;

FIG. 10 is a timing diagram showing an example of variations of anengine resistive torque as a function of time along with correspondingengine rotational speed variations;

FIG. 11 is a logic diagram of a method for starting the engine of FIG. 2according to another implementation;

FIG. 12 is a circuit diagram showing connections between the inverter,the capacitance and the motor-generator of FIG. 6;

FIG. 13 is a block diagram of a typical implementation of a vectorcontrol drive;

FIG. 14 is a block diagram of an electric system according to animplementation of the present technology;

FIG. 15 is a timing diagram showing an example of a sequence forchanging the control strategy for the delivery of electric power betweenthe capacitance and the electric turning machine (ETM) along withcorresponding engine rotational speed variations; and

FIG. 16 is another timing diagram showing an example of an impact of thecontrol strategies on a current exchanged between the capacitance andthe ETM and on a system voltage.

DETAILED DESCRIPTION

The method and system for starting an internal combustion engine (ICE)and the method and system for an assisted start of the ICE will bedescribed with respect to a snowmobile 10. However, it is contemplatedthat the method and system could be used in other vehicles, such as, butnot limited to, on-road vehicles, off-road vehicles, a motorcycle, ascooter, a three-wheel road vehicle, a boat powered by an outboardengine or an inboard engine, and an all-terrain vehicle (ATV). It isalso contemplated that the method and system could be used in devicesother than vehicles that have an internal combustion engine such as agenerator. The method and system will also be described with respect toa two-stroke, inline, two-cylinder internal combustion engine (ICE) 24.However, it is contemplated that the method and system could be usedwith an internal combustion engine having one or more cylinders and, inthe case of multi-cylinder engines, having an inline or otherconfiguration, such as a V-type engine as well as 4-stroke engines.

Vehicle

Turning now to FIG. 1, a snowmobile 10 includes a forward end 12 and arearward end 14 that are defined consistently with a forward traveldirection of the snowmobile 10. The snowmobile 10 includes a frame 16that has a tunnel 18, an engine cradle portion 20 and a front suspensionassembly portion 22. The tunnel 18 consists of one or more pieces ofsheet metal arranged to form an inverted U-shape that is connected atthe front to the engine cradle portion 20 and extends rearward therefromalong the longitudinal axis 23. An ICE 24 (schematically illustrated inFIG. 1) is carried by the engine cradle portion 20 of the frame 16. TheICE 24 is described in greater detail below. Two skis 26 are positionedat the forward end 12 of the snowmobile 10 and are attached to the frontsuspension assembly portion 22 of the frame 16 through a frontsuspension assembly 28. The front suspension assembly 28 includes shockabsorber assemblies 29, ski legs 30, and supporting arms 32. Ball jointsand steering rods (not shown) operatively connect the skis 26 to asteering column 34. A steering device in the form of handlebar 36 isattached to the upper end of the steering column 34 to allow a driver torotate the ski legs 30 and thus the skis 26, in order to steer thesnowmobile 10.

An endless drive track 38 is disposed generally under the tunnel 18 andis operatively connected to the ICE 24 through a CVT 40 (schematicallyillustrated by broken lines in FIG. 1) which will be described ingreater detail below. The endless drive track 38 is driven to run abouta rear suspension assembly 42 for propulsion of the snowmobile 10. Therear suspension assembly 42 includes a pair of slide rails 44 in slidingcontact with the endless drive track 38. The rear suspension assembly 42also includes a plurality of shock absorbers 46 which may furtherinclude coil springs (not shown) surrounding one or more of the shockabsorbers 46. Suspension arms 48 and 50 are provided to attach the sliderails 44 to the frame 16. A plurality of idler wheels 52 are alsoprovided in the rear suspension assembly 42. Other types and geometriesof rear suspension assemblies are also contemplated.

At the forward end 12 of the snowmobile 10, fairings 54 enclose the ICE24 and the CVT 40, thereby providing an external shell that protects theICE 24 and the CVT 40. The fairings 54 include a hood and one or moreside panels that can be opened to allow access to the ICE 24 and the CVT40 when this is required, for example, for inspection or maintenance ofthe ICE 24 and/or the CVT 40. A windshield 56 is connected to thefairings 54 near the forward end 12 of the snowmobile 10. Alternativelythe windshield 56 could be connected directly to the handlebar 36. Thewindshield 56 acts as a wind screen to lessen the force of the air onthe driver while the snowmobile 10 is moving forward.

A straddle-type seat 58 is positioned over the tunnel 18. Two footrests60 are positioned on opposite sides of the snowmobile 10 below the seat58 to accommodate the driver's feet.

Internal Combustion Engine

Turning now to FIGS. 2 to 5, the ICE 24 and the CVT 40 will bedescribed. The ICE 24 operates on the two-stroke principle. The ICE 24has a crankshaft 100 that rotates about a horizontally disposed axisthat extends generally transversely to the longitudinal axis 23 of thesnowmobile 10. The crankshaft drives the CVT 40 for transmitting torqueto the endless drive track 38 for propulsion of the snowmobile 10.

The CVT 40 includes a drive pulley 62 coupled to the crankshaft 100 torotate with the crankshaft 100 and a driven pulley (not shown) coupledto one end of a transversely mounted jackshaft (not shown) that issupported on the frame 16 through bearings. The opposite end of thetransversely mounted jackshaft is connected to the input member of areduction drive (not shown) and the output member of the reduction driveis connected to a drive axle (not shown) carrying sprocket wheels (notshown) that form a driving connection with the drive track 38.

The drive pulley 62 of the CVT 40 includes a pair of opposedfrustoconical belt drive sheaves 64 and 66 between which a drive belt(not shown) is located. The drive belt is made of rubber, but it iscontemplated that it could be made of metal linkages or of a polymer.The drive pulley 62 will be described in greater detail below. Thedriven pulley includes a pair of frustoconical belt drive sheavesbetween which the drive belt is located. The drive belt is looped aroundboth the drive pulley 62 and the driven pulley. The torque beingtransmitted to the driven pulley provides the necessary clamping forceon the drive belt through its torque sensitive mechanical device inorder to efficiently transfer torque to the other powertrain components.

As discussed above, the drive pulley 62 includes a pair of opposedfrustoconical belt drive sheaves 64 and 66 as can be seen in FIG. 5.Both sheaves 64 and 66 rotate together with the crankshaft 100. Thesheave 64 is fixed in an axial direction relative to the crankshaft 100,and is therefore referred to as the fixed sheave 64. The fixed sheave 64is also rotationally fixed relative to the crankshaft 100. The sheave 66can move toward or away from the fixed sheave 64 in the axial directionof the crankshaft 100 in order to change the drive ratio of the CVT 40,and is therefore referred to as the movable sheave 66. As can be seen inFIG. 5, the fixed sheave 64 is disposed between the movable sheave 66and the ICE 24.

The fixed sheave 64 is mounted on a fixed sheave shaft 68. The fixedsheave 64 is press-fitted on the fixed sheave shaft 68 such that thefixed sheave 64 rotates with the fixed sheave shaft 68. It iscontemplated that the fixed sheave 64 could be connected to the fixedsheave shaft 68 in other known manners to make the fixed sheave 64rotationally and axially fixed relative to the fixed sheave shaft 68. Ascan be seen in FIG. 5, the fixed sheave shaft 68 is hollow and has atapered hollow portion. The tapered hollow portion receives the end ofthe crankshaft 100 therein to transmit torque from the ICE 24 to thedrive pulley 62. A fastener 70 is inserted in the outer end (i.e. theleft side with respect to FIG. 5) of the drive pulley 62, inside thefixed sheave shaft 68, and screwed into the end of the crankshaft 100 toprevent axial displacement of the fixed sheave shaft 68 relative to thecrankshaft 100. It is contemplated that the fixed sheave shaft 68 couldbe connected to the crankshaft 100 in other known manners to make thefixed sheave shaft 68 rotationally and axially fixed relative to thecrankshaft 100. It is also contemplated that the crankshaft 100 could bethe fixed sheave shaft 68.

A cap 72 is taper-fitted in the outer end of the fixed sheave shaft 68.The fastener 70 is also inserted through the cap 72 to connect the cap72 to the fixed sheave shaft 68. It is contemplated that the cap 72could be connected to the fixed sheave shaft 68 by other means. Theradially outer portion of the cap 72 forms a ring 74. An annular rubberdamper 76 is connected to the ring 74. Another ring 78 is connected tothe rubber damper 76 such that the rubber damper 76 is disposed betweenthe rings 74, 78. In the present implementation, the rubber damper 76 isvulcanized to the rings 74, 78, but it is contemplated that they couldbe connected to each other by other means such as by using an adhesivefor example. It is also contemplated that the damper 76 could be made ofa material other than rubber.

A spider 80 is disposed around the fixed sheave shaft 68 and axiallybetween the ring 78 and the movable sheave 66. The spider 80 is axiallyfixed relative to the fixed sheave 64. Apertures (not shown) are formedin the ring 74, the damper 76, and the ring 78. Fasteners (not shown)are inserted through the apertures in the ring 74, the damper 76, thering 78 and the spider 80 to fasten the ring 78 to the spider 80. As aresult, torque is transferred between the fixed sheave shaft 68 and thespider 80 via the cap 72, the rubber damper 76 and the ring 78. Thedamper 76 dampens the torque variations from the fixed sheave shaft 68resulting from the combustion events in the ICE 24. The spider 80therefore rotates with the fixed sheave shaft 68.

A movable sheave shaft 82 is disposed around the fixed sheave shaft 68.The movable sheave 66 is press-fitted on the movable sheave shaft 82such that the movable sheave 66 rotates and moves axially with themovable sheave shaft 82. It is contemplated that the movable sheave 66could be connected to the movable sheave shaft 82 in other known mannersto make the movable sheave 66 rotationally and axially fixed relative tothe shaft 82. It is also contemplated that the movable sheave 66 and themovable sheave shaft 82 could be integrally formed.

To transmit torque from the spider 80 to the movable sheave 104, atorque transfer assembly consisting of three roller assemblies 84connected to the movable sheave 66 is provided. The roller assemblies 84engage the spider 80 so as to permit low friction axial displacement ofthe movable sheave 66 relative to the spider 80 and to eliminate, or atleast minimize, rotation of the movable sheave 66 relative to the spider80. As described above, torque is transferred from the fixed sheave 64to the spider 80 via the damper 76. The spider 80 engages the rollerassemblies 84 which transfer the torque to the movable sheave 66 withno, or very little, backlash. As such, the spider 80 is considered to berotationally fixed relative to the movable sheave 66. It is contemplatedthat in some implementations, the torque transfer assembly could havemore or less than three roller assemblies 84.

As can be seen in FIG. 5, a biasing member in the form of a coil spring86 is disposed inside a cavity 88 defined radially between the movablesheave shaft 82 and the spider 80. As the movable sheave 66 and themovable sheave shaft 82 move axially toward the fixed sheave 64, thespring 86 gets compressed. The spring 86 biases the movable sheave 66and the movable sheave shaft 82 away from the fixed sheave 64 towardtheir position shown in FIG. 5. It is contemplated that, in someimplementations, the movable sheave 66 could be biased away from thefixed sheave 64 by mechanisms other than the spring 86.

The spider 80 has three arms 90 disposed at 120 degrees from each other.Three rollers 92 are rotatably connected to the three arms 90 of thespider 80. Three centrifugal actuators 94 are pivotally connected tothree brackets (not shown) formed by the movable sheave 66. Each roller92 is aligned with a corresponding one of the centrifugal actuators 94.Since the spider 80 and the movable sheave 66 are rotationally fixedrelative to each other, the rollers 92 remain aligned with theircorresponding centrifugal actuators 94 when the shafts 68, 82 rotate.The centrifugal actuators 94 are disposed at 120 degrees from eachother. The centrifugal actuators 94 and the roller assemblies 84 arearranged in an alternating arrangement and are disposed at 60 degreesfrom each other. It is contemplated that the rollers 92 could bepivotally connected to the brackets of the movable sheave 66 and thatthe centrifugal actuators 94 could be connected to the arms 90 of thespider 80. It is also contemplated that there could be more or less thanthree centrifugal actuators 94, in which case there would be acorresponding number of arms 90, rollers 92 and brackets of the movablesheave. It is also contemplated that the rollers 92 could be omitted andreplaced with surfaces against which the centrifugal actuators 94 canslide as they pivot.

In the present implementation, each centrifugal actuator 94 includes anarm 96 that pivots about an axle 98 connected to its respective bracketof the movable sheave 66. The position of the arms 96 relative to theiraxles 98 can be adjusted. It is contemplated that the position of thearms 96 relative to their axles 98 could not be adjustable. Additionaldetail regarding centrifugal actuators of the type of the centrifugalactuator 94 can be found in International Patent Publication No.WO2013/032463 A2, published Mar. 7, 2013, the entirety of which isincorporated herein by reference.

The above description of the drive pulley 62 corresponds to onecontemplated implementation of a drive pulley that can be used with theICE 24. Additional detail regarding drive pulleys of the type of thedrive pulley 62 can be found in International Patent Publication No. WO2015/151032 A1, published on Oct. 8, 2015, the entirety of which isincorporated herein by reference. It is contemplated that other types ofdrive pulleys could be used.

The ICE 24 has a crankcase 102 housing a portion of the crankshaft 100.As can be seen in FIGS. 2, 3 and 5, the crankshaft 100 protrudes fromthe crankcase 102. It is contemplated that the crankshaft 100 coulddrive an output shaft connected directly to the end of the crankshaft100 or offset from the crankshaft 100 and driven by driving means suchas gears in order to drive the drive pulley 62. It is also contemplatedthat the crankshaft 100 could drive, using gears for example, acounterbalance shaft housed in part in the crankcase 102 and that thedrive pulley 62 could be connected to the counterbalance shaft, in whichcase, the crankshaft 100 does not have to protrude from the crankcase102 for this purpose. A cylinder block 104 is disposed on top of andconnected to the crankcase 102. The cylinder block 104 as shown definestwo cylinders 106A, 106B (FIG. 5). A cylinder head 108 is disposed ontop of and is connected to the cylinder block 104.

As best seen in FIG. 5, the crankshaft 100 is supported in the crankcase102 by bearings 110. The crankshaft 100 has two crank pins 112A, 112B.In the illustrated implementation where the two cylinders 106A, 106B aredisposed in line, the crank pins 112A, 112B are provided at 180 degreesfrom each other. It is contemplated that the crank pins 112A, 112B couldbe provided at other angles from each other to account for othercylinder arrangements, such as in a V-type engine. A connecting rod 114Ais connected to the crank pin 112A at one end and to a piston 116A via apiston pin 118A at the other end. As can be seen, the piston 116A isdisposed in the cylinder 106A. Similarly, a connecting rod 114B isconnected to the crank pin 112B at one end and to a piston 116B via apiston pin 118B at the other end. As can be seen, the piston 116B isdisposed in the cylinder 106B. Rotation of the crankshaft 100 causes thepistons 116A, 116B to reciprocate inside their respective cylinders106A, 106B. The cylinder head 108, the cylinder 106A and the piston 116Adefine a variable volume combustion chamber 120A therebetween.Similarly, the cylinder head 108, the cylinder 106B and the piston 116Bdefine a variable volume combustion chamber 120B therebetween. It iscontemplated that the cylinder block 104 could define more than twocylinders 106, in which case the ICE 24 would be provided with acorresponding number of pistons 116 and connecting rods 114.

Air is supplied to the crankcase 102 via a pair of air intake ports 122(only one of which is shown in FIG. 4) formed in the back of thecylinder block 104. A pair of throttle bodies 124 is connected to thepair of air intake ports 122. Each throttle body 124 has a throttleplate 126 that can be rotated to control the air flow to the ICE 24.Motors (not shown) are used to change the position of the throttleplates 126, but it is contemplated that throttle cables connected to athrottle lever could be used. It is also contemplated that a singlemotor could be used to change the position of both throttle plates 126.A pair of reed valves 128 (FIG. 4) are provided in each intake port 122.The reed valves 128 allow air to enter the crankcase 102, but preventair from flowing out of the crankcase 102 via the air intake ports 122.

As the pistons 116A, 116B reciprocate, air from the crankcase 102 flowsinto the combustion chambers 120A, 120B via scavenge ports 130. Fuel isinjected in the combustion chambers 120A, 120B by fuel injectors 132 a,132 b respectively. The fuel injectors 132 a, 132 b are mounted to thecylinder head 108. The fuel injectors 132 a, 132 b are connected by fuellines and/or rails (not shown) to one or more fuel pumps (not shown)that pump fuel from a fuel tank 133 (FIG. 1) of the snowmobile 10. Inthe illustrated implementation, the fuel injectors 132 a, 132 b areE-TEC™ direct fuel injectors, however other types of injectors arecontemplated. The fuel-air mixture in the combustion chamber 120A, 120Bis ignited by spark plugs 134 a, 134 b respectively (not shown in FIGS.2 to 5, but schematically illustrated in FIG. 6). The spark plugs 134 a,134 b are mounted to the cylinder head 108.

To evacuate the exhaust gases resulting from the combustion of thefuel-air mixture in the combustion chambers 120A, 120B, each cylinder116A, 116B defines one main exhaust port 136A, 136B respectively and twoauxiliary exhaust ports 138A, 138B respectively. It is contemplated thateach cylinder 116A, 116B could have only one, two or more than threeexhaust ports. The exhaust ports 136A, 136B (FIG. 4), 138A, 138B areconnected to an exhaust manifold 140. The exhaust manifold is connectedto the front of the cylinder block 104. Exhaust valves 142A, 142Bmounted to the cylinder block 104, control a degree of opening of theexhaust ports 136A, 136B, 138A, 138B. In the present implementation, theexhaust valves 142A, 142B are R.A.V.E.™ exhaust valves, but other typesof valves are contemplated. It is also contemplated that the exhaustvalves 142A, 142B could be omitted.

An electric turning machine (ETM) is connected to the end of thecrankshaft 100 opposite the end of the crankshaft 100 that is connectedto the drive pulley 62. In the present implementation, the ETM is amotor-generator 144 (FIG. 5), and more specifically a three-phasealternating current motor-generator 144, such as a permanent magnetmotor for example. It is contemplated that the motor-generator mayinclude a number of pole pairs, generating electric power cycling at arate that is a multiple of the rotational speed of the crankshaft 100.It is further contemplated that other types of motor-generators could beused, including for example multi-phase motor-generators or poly-phasemotor-generators. It is also contemplated that the motor-generator 144could be connected to another shaft operatively connected to thecrankshaft 100, by gears or belts for example. The motor-generator 144,as its name suggests, can act as a motor or as a generator and can beswitched between either functions. Under certain conditions as describedhereinbelow, the motor-generator 144 is operated in motor operatingmode, being powered either by a small battery (not shown) or by acapacitance 145 (shown on FIG. 6).

A battery that is smaller and lighter than one conventionally used forcold starting of the ICE 24 may be used for an electric start procedureand/or for an assisted start procedure that will be describedhereinbelow. Alternatively, the electric start procedure and/or theassisted start procedure may rely on the use of a capacitance 145.Non-limiting examples of capacitances include a high-capacity capacitor,an ultracapacitor (U-CAP), an electric double layer capacitor and asupercapacitor Either the small battery or the capacitance 145 supplieselectric power to the motor-generator 144 for turning the crankshaft100. The capacitance 145 can accumulate relatively large amounts ofenergy. In at least one implementation, the capacitance 145 comprises aplurality of capacitors assembled in series, each capacitor of theseries possibly including several capacitors mounted in parallel so thatthe capacitance 145 can withstand voltages generally within an operatingvoltage range of direct fuel injectors. In the context of the presentdisclosure, references are made to the capacitance 145 as a single unit.Without limitation and for brevity, implementations in which theelectric start procedure or the assisted start procedure, or both, areimplemented using the capacitance 145 along with the motor-generator 144will be described hereinbelow.

When operating as a generator, the motor-generator 144 is turned by thecrankshaft 100 and generates electricity that is supplied to thecapacitance 145 and to other electrical components of the ICE 24 and thesnowmobile 10. Electric power is exchanged between the capacitance 145and the motor-generator 144 through an electrical converter. Inimplementations in which the motor-generator 144 is a three-phase motor,the electrical converter is a three-phase inverter 146. Use ofmulti-phase or poly-phase invertors in cooperation with a multi-phase ora poly-phase motor-generator is also contemplated. Control strategies ofthe motor-generator 144 applicable to its motoring and generatingfunctions and the impact of these strategies on the capacitance 145 andon the inverter 146 are described hereinbelow.

As can be seen in FIG. 5, the motor-generator 144 has a stator 148 and arotor 150. The stator 148 is disposed around the crankshaft 100 outsideof the crankcase 102 and is fastened to the crankcase 102. The rotor 150is connected by splines to the end of the crankshaft 100 and partiallyhouses the stator 148. A housing 152 is disposed over themotor-generator 144 and is connected to the crankcase 102. A cover 154is connected to the end of the housing 152.

Three starting procedures of the snowmobile 10 may be available to theuser. A first procedure comprises a manual start procedure that relieson the use of a recoil starter 156. A second starting procedurecomprises an electric start procedure. A third starting procedurecomprises an assisted start procedure. One or both of the electric andassisted start procedures may be present in any implementation of thesnowmobile 10. The second and third starting procedures will bedescriber further below. As can be seen in FIG. 5, the recoil starter156 is disposed inside the space defined by the housing 152 and thecover 154, between the cover 154 and the motor-generator 144. The recoilstarter 156 has a rope 158 wound around a reel 160. A ratchetingmechanism 162 selectively connects the reel 160 to the rotor 150. Tostart the ICE 24 using the recoil starter 156 in the manual startprocedure, a user pulls on a handle 163 (FIG. 3) connected to the end ofthe rope 158. This turns the reel 160 in a direction that causes theratcheting mechanism 162 to lock, thereby turning the rotor 150 and thecrankshaft 100. The rotation of the crankshaft 100 causes the pistons116A, 116B to reciprocate which permits fuel injection and ignition tooccur, thereby starting the ICE 24. When the ICE 24 starts, the rotationof the crankshaft 100 relative to the reel 160 disengages the ratchetingmechanism 162, and as such the crankshaft 100 does not turn the reel160. When the user releases the handle, a spring (not shown) turns thereel 160 thereby winding the rope 158 around the reel 160.

In the present implementation, the drive pulley 62 and themotor-generator 144 are both mounted to the crankshaft 100. It iscontemplated that the drive pulley 62 and the motor-generator 144 couldboth be mounted to a shaft other than the crankshaft 100, such as acounterbalance shaft for example. In the present implementation, thedrive pulley 62, the motor-generator 144 and the recoil starter 56 areall coaxial with and rotate about the axis of rotation of the crankshaft100. It is contemplated that the drive pulley 62, the motor-generator144 and the recoil starter 56 could all be coaxial with and rotate aboutthe axis of rotation of a shaft other than the crankshaft 100, such as acounterbalance shaft for example. It is also contemplated that at leastone of the drive pulley 62, the motor-generator 144 and the recoilstarter 56 could rotate about a different axis. In the presentimplementation, the drive pulley 62 is disposed on one side of the ICE24 and the motor-generator 144 and the recoil starter 56 are bothdisposed on the other side of the ICE 24. It is contemplated the motorgenerator and/or the recoil starter 56 could be disposed on the sameside of the ICE 24 as the drive pulley 62.

Control System for the Internal Combustion Engine

Available starting procedures of the snowmobile 10 comprise an electricstart procedure, an assisted start procedure and a manual startprocedure. FIG. 6 is a schematic diagram of components of a controlsystem of the engine of FIG. 2. The control of the components used tostart the ICE 24 in the electric start procedure and in the assistedstart procedure is done by an engine control unit (ECU) 164 as will beexplained below. The ECU 164 is also used to control the operation ofthe ICE 24 after it has started. The ECU 164 is illustrated as a singlephysical module (later shown in FIG. 14) comprising a single processor(also in FIG. 14), for example a single microcontroller. Otherconfigurations are within the scope of the present disclosure. Forinstance, it is contemplated that features of the ECU 164 may beimplemented using a plurality of co-processors, for example two or moremicrocontrollers. It is also contemplated that the various tasks of theECU 164 could be split between two or more microprocessors integrated ina single electronic module or two or more microprocessors distributedamong various electronic modules. As a non-limitative example, thesingle electronic module may comprise a first processor adapted forcontrolling a delivery of electric power from the motor-generator 144 tothe capacitance 145 and to control the delivery of electric power fromthe capacitance 145 to the motor-generator 144, and a second processoradapted for controlling a fuel injection function and an ignitionfunction of the ICE. To initiate an electric start procedure or anassisted start procedure of the ICE 24, the ECU 164 receives inputs fromthe components disposed to the left of the ECU 164 in FIG. 6, some ofwhich are optional and not present in all implementations, as will bedescribed below. Using these inputs, the ECU 164 obtains informationfrom control maps 166 as to how the components disposed to the right ofthe ECU 164 in FIG. 6 should be controlled in order to start the ICE 24.The control maps 166 are stored in an electronic data storage device,such as a static random access memory (SRAM), an electrically-erasableprogrammable read-only memory (EEPROM) or a flash drive. It iscontemplated that instead of or in addition to the control maps 166, theECU 164 could use control algorithms to control the components disposedto the right of the ECU 164 in FIG. 6. In the present implementation,the ECU 164 is connected with the various components illustrated in FIG.6 via wired connections; however it is contemplated that it could beconnected to one or more of these components wirelessly.

A user actionable electric start switch 168, provided on the snowmobile10, for example a push button mounted on or near the handlebar 36, sendsa signal to the ECU 164 that the user desires the ICE 24 to start whenit is actuated. The electric start switch 168 can also be a switchactuated by a key, a sensor, or any other type of device through whichthe user can provide an input to the ECU 164 that the ICE 24 is to bestarted. In at least one implementation, the electric start switch 168may be a sensor operably connected to the rope 158 of the recoil starter156 and to the ECU 164. Some traction, for example a simple tugging onthe rope 158 by an operator, may be detected by this sensor, resultingin the initiation of the electric start procedure of the ICE 24,provided that all conditions for the electric start procedure arepresent.

A crankshaft position sensor 170 is disposed in the vicinity of thecrankshaft 100 in order to sense the position of the crankshaft 100. Thecrankshaft position sensor 170 sends a signal representative of theposition of the crankshaft 100 to the ECU 164. In the presentimplementation, the crankshaft position sensor 170 is an absoluteposition sensor, such as a sin/cos Hall Effect encoder for example.Based on the change in the signal received from the crankshaft positionsensor 170, the ECU 164 is also able to determine an angular position ofthe crankshaft 100. It is contemplated that the crankshaft positionsensor 170 could alternatively sense the position of an element otherthan the crankshaft 100 that turns with the crankshaft 100, such as therotor 150 of the motor-generator 144 for example, and be able todetermine the position of the crankshaft 100 from the position of thiselement. Use of a relative position sensor to sense the position of thecrankshaft 170 is also contemplated as expressed hereinbelow.

The assisted start procedure may be initiated, provided that conditionsare met as described hereinbelow, when a rotation of the crankshaft 100is initiated by the user pulling on the rope 158 of the recoil starter156. The crankshaft position sensor 170 informs the ECU 170 of therotation of the crankshaft 100.

A voltage sensor 167, for example a voltmeter, provides a measurement ofa voltage of the capacitance 145 to the ECU 164. As explained in moredetails hereinbelow, the ECU 164 uses this voltage measurement todetermine whether an energy reserve of the capacitance 145 is sufficientto start the ICE 24 using the electric start procedure or to provideassist using the assisted start procedure.

Optionally, other sensors can be used to determine whether or not theengine can be started using the electric start procedure or the assistedstart procedure as expressed hereinbelow. These optional sensors includefor example an engine temperature sensor 172, an air temperature sensor174, an atmospheric air pressure sensor 176, an exhaust temperaturesensor 178, a timer 180 and an ECU temperature sensor 182.

The engine temperature sensor 172 is mounted to the ICE 24 to sense thetemperature of one or more of the crankcase 102, the cylinder block 104,the cylinder head 108 and engine coolant temperature. The enginetemperature sensor 172 sends a signal representative of the sensedtemperature to the ECU 164.

The air temperature sensor 174 is mounted to the snowmobile 10, in theair intake system for example, to sense the temperature of the air to besupplied to the ICE 24. The air temperature sensor 174 sends a signalrepresentative of the air temperature to the ECU 164.

The atmospheric air pressure sensor 176 is mounted to the snowmobile 10,in the air intake system for example, to sense the atmospheric airpressure. The atmospheric air pressure sensor 176 sends a signalrepresentative of the atmospheric air pressure to the ECU 164.

The exhaust temperature sensor 178 is mounted to the exhaust manifold140 or another portion of an exhaust system of the snowmobile 10 tosense the temperature of the exhaust gases. The exhaust temperaturesensor 178 sends a signal representative of the temperature of theexhaust gases to the ECU 164.

The timer 180 is connected to the ECU 164 to provide information to theECU 164 regarding the amount of time elapsed since the ICE 24 hasstopped. The timer 180 can be an actual timer which starts when the ICE24 stops. Alternatively, the function of the timer 180 can be obtainedfrom a calendar and clock function of the ECU 164 or another electroniccomponent. In such an implementation, the ECU 164 logs the time and datewhen the ICE 24 is stopped and looks up this data to determine how muchtime has elapsed since the ICE 24 has stopped when the ECU 164 receivesa signal from the electric start switch 168 that the user desires theICE 24 to be started.

The ECU temperature sensor 182 is mounted to a physical module (notshown) that includes one or more processors (not shown) configured toexecute the functions of the ECU 164. The ECU temperature sensor 182sends a signal representative of the temperature of that module to theECU 164.

It is contemplated that one or more of the sensors 172, 174, 176, 178,182 and the timer 180 could be omitted. It is also contemplated that oneor more of the sensors 172, 174, 176, 178, 180, 182 and the timer 180could be used only under certain conditions. For example, the exhausttemperature and pressure sensors 178, 180 may only be used if the ICE 24has been recently stopped, in which case some exhaust gases would stillbe present in the exhaust system, or following the first combustion of afuel-air mixture in one of the combustion chambers 120A, 120B.

The ECU 164 uses the inputs received from at least some of the electricstart switch 168, the sensors 167, 170, 172, 174, 176, 178, 182 and thetimer 180 to retrieve one or more corresponding control maps 166 and tocontrol the motor-generator 144, the fuel injectors 132 a, 132 b, andthe spark plugs 134 a, 134 b using these inputs and/or the control maps166 to start the ICE 24, as the case may be. The inputs and control maps166 are also used to control the operation of the ICE 24 once it hasstarted.

The ECU 164 is also connected to a display 186 provided on thesnowmobile 10 near the handlebar 36 to provide information to the userof the snowmobile 10, such as engine speed, vehicle speed, oiltemperature, and fuel level, for example.

Turning now to FIG. 7, details of an electronic system for the electricand assisted start procedures for the ICE 24 will now be described. FIG.7 is a block diagram of a dual-strategy control system for delivery ofelectric power between the capacitance and the ETM of FIG. 6. Somecomponents introduced in the foregoing description of FIG. 6 arereproduced in FIG. 7 in order to provide more details on theiroperation.

Electric power is delivered between the capacitance 145 and themotor-generator 144 through the inverter 146. The ECU 164 includes, oris otherwise operatively connected to, a strategy switch 184 that isoperative to change the control strategy for the delivery of electricpower between the capacitance 145 and the motor-generator 144 between atleast two (2) distinct control strategies. The ECU 164 controls theinverter 146 through the strategy switch 184.

To start the ICE 24 using the electric start procedure, the user of thesnowmobile 10 enters an input on the electric start switch 168, forexample by depressing a push button. The ECU 164 is informed of thiscommand. In response, the ECU 164 may control a delivery of electricpower from the capacitance 145 to the motor-generator 144 based on apre-determined amount of torque, or torque request, sufficient to causerotation of the crankshaft 100 for starting the ICE 24. In a variant,the ECU 164 may determine the torque request. The determination of thetorque request is made considering that ICE 24 is expected to have ahighly irregular resistive torque; alternatively, instead of determiningthe torque request, the ECU 164 may determine a speed request applicableto the crankshaft 100 to control an amount of power that that themotor-generator 144 should apply to the crankshaft 100 for starting theICE 24. A voltage of the capacitance 145 is sensed by the voltage sensor167 and provided to the ECU 164. If this voltage is below an electricstart voltage threshold V_(MinE), which is a minimum voltage of thecapacitance 145 for the electric start procedure, the ECU 164 determinesthat the capacitance 145 does not hold sufficient energy to provide thetorque request, or the speed request, sufficient to start the ICE 24using the electric start procedure. Consequently, the ECU 164 does notallow starting the ICE 24 using the electric start procedure and causesthe display 186 to show a “manual start” indication or an “assistedstart” indication, in implementations where this option is available.Generally speaking, the electric start voltage threshold V_(MinE) isbased on a determination of a sufficient charge of the capacitance 145allowing a successful electric start procedure in most operatingconditions. If this minimum voltage threshold for the electric startprocedure is met, the ECU 164 causes delivery of electric power from thecapacitance 145 to the motor-generator 144, via the inverter 146, in afirst control strategy, initiating a rotation of the crankshaft 100. TheECU 164 also causes the fuel injectors 132 a and 132 b to inject fuel inthe combustion chambers 120A, 120B and causes the spark plugs 134 a and134 b to ignite the fuel in the combustion chambers 120A, 120B. Asmentioned hereinabove, the ICE 24 may comprise one or more cylinders andthe mention of two (2) combustion chambers 120A and 120B is forexplanation purposes only. If these operations are successful, therotation of the crankshaft 100 reaches a minimum revolution thresholdcorresponding to a successful start of the ICE 24. Thereafter, when aspeed of the crankshaft 100 is equal to or above the minimum revolutionthreshold, the ECU 164 controls the delivery of electric power from themotor-generator 144 to the capacitance 145, still via the inverter 146,to cause charging of the capacitance 145. The delivery of electric powerfrom the motor-generator 144 to the capacitance 145 generally occurs ina second control strategy distinct from the first control strategy. Avariant in which the delivery of electric power from the motor-generator144 to the capacitance 145 occurs in the first control strategy at lowrevolution speeds of the crankshaft 100, or under low throttle demands,and in the second control strategy at high revolution speeds of thecrankshaft 100 is also contemplated.

A current sensor 188 may be used to optimize the capacitance 145 currentconsumption and optimize its energy usage. The current sensor 188provides to the ECU 164 an indication of the energy from the capacitance145 being consumed during the electric start procedure. In animplementation, the current sensor 188 comprises a combination of phasecurrent sensors (not explicitly shown) provided on two (2) phases of themotor-generator 144. Encoding of measurements from these two (2) phasecurrent sensors provide a good estimation of a current flowing betweenthe capacitance 145 and the motor-generator 144. As shown on FIG. 13,current measurements may be obtained on all three (3) phases of themotor-generator 144. The capacitance 145 energy usage can alternativelybe optimized without current sensors, for example, an open loop approachhaving a predetermined torque request pattern being applied by the ECU164 to drive all cranking sequences can be used. It is also possible tooptimize the energy usage of the capacitance 145 based on a speedrequest with well-tuned regulators or based on a predetermined patternof multistep speed requests.

Electric start of the ICE 24 may fail although initial conditions forthe electric start procedure were initially present. This may occur forinstance if, while electric power is being delivered from thecapacitance 145 to the motor-generator 144, the voltage sensor 167detects that the voltage of the capacitance 145 falls below a residualvoltage threshold V_(MinR), lower than the electric start voltagethreshold V_(MinE), before the rotational speed of the crankshaft 100reaches the minimum revolution threshold corresponding to the successfulstart of the ICE 24. Under such conditions, the ECU 164 ceases thedelivery of power from the capacitance 145 to the motor-generator 144and causes the display 186 to provide a manual start indication or anassisted start indication, in implementations where this option isavailable. Generally speaking, the residual voltage threshold V_(MinR)corresponds to a minimum charge of the capacitance 145 that is expectedto suffice in allowing the injection and ignition of fuel injection inthe combustion chambers 120A, 120B while continuing the rotation of thecrankshaft 100.

To start the ICE 24 using the assisted start procedure, the user of thesnowmobile 10 pulls on the rope 158 of the recoil starter 156,initiating a rotation of the crankshaft 100. The crankshaft positionsensor 170 informs the ECU 170 of the rotation of the crankshaft 100. Inresponse, the ECU 164 may control a delivery of electric power from thecapacitance 145 to the motor-generator 144 to assist the rotation of thecrankshaft 100 for starting the ICE 24. Optionally, a voltage of thecapacitance 145 is sensed by the voltage sensor 167 and provided to theECU 164. In this case, if this voltage is below an assisted startvoltage threshold V_(MinA), which is a minimum voltage of thecapacitance 145 for the assisted start procedure, the ECU 164 determinesthat the capacitance 145 does not hold sufficient energy to assiststarting the ICE 24 and the ECU 164 does not allow starting the ICE 24using the assisted start procedure, instead causing the display 186 toshow a “manual start” indication. Generally speaking, the assisted startvoltage threshold V_(MinA) is based on a determination of a sufficientcharge of the capacitance 145 allowing a successful assisted startprocedure in predetermined operating conditions. In implementationswhere both electric and assisted start procedures are present, theassisted start voltage threshold V_(MinA) is lower than the electricalstart voltage threshold V_(MinE). If this minimum voltage threshold forthe assisted start procedure is met, the ECU 164 causes delivery ofelectric power from the capacitance 145 to the motor-generator 144, viathe inverter 146, in the first control strategy, assisting the rotationof the crankshaft 100. The ECU 164 also causes the fuel injectors 132 aand 132 b to inject fuel in the combustion chambers 120A, 120B andcauses the spark plugs 134 a and 134 b to ignite the fuel in thecombustion chambers 120A, 120B. As mentioned hereinabove, the ICE 24 maycomprise one or more cylinders and the mention of two (2) combustionchambers 120A and 120B is for explanation purposes only. If theseoperations are successful, the rotation of the crankshaft 100 reaches aminimum revolution threshold corresponding to a successful start of theICE 24. Thereafter, operation of the ICE 24 is as expressed in theforegoing description to the electrical start procedure.

FIG. 8 is a block diagram of an energy management circuit for thecapacitance 145 of FIG. 6. A circuit 200 shows how, in animplementation, the ECU 164 and the capacitance 145 are electricallyconnected using the electric start switch 168, which is shown as apushbutton. The capacitance 145 is illustrated as a sum of smallercapacitors 202 connected in series. As mentioned earlier, each of thesesmaller capacitors 202 may actually consist of a plurality of capacitorsconnected in parallel. Each of the smaller capacitors 202 can withstanda relatively low voltage applied thereon. The capacitance 145 formed bythe sum of the smaller capacitors 202 in series can withstand thenominal voltage of the circuit 200, which is also the nominal voltage ofthe electrical systems of the snowmobile 10, with the addition of asafety margin for occasional overvoltage. The voltage present on thecapacitance 145 is defined between terminals 204 and 206 that areelectrically connected to the voltage sensor 167 shown on earlierFigures.

The circuit 200 provides an output voltage between a lead 208 and aground reference 210 when the circuit 200 is active. When the circuit200 is inactive, the capacitance 145 is disconnected from the groundreference 210 by a metal-oxide semiconductor field effect transistor(MOSEFT) Q1 which is, at the time, turned off and therefore opencircuit. Substituting a bipolar transistor, for example an insulatedgate bipolar transistor (IGBT), for the MOSFET Q1 is also contemplated.

A capacitor C1 is present between the lead 208 and the ground reference210. The role of the capacitor C1 is to filter voltage variations at theoutput 204 for the benefit of the various electrical components of thesnowmobile 10, including for example the fuel injectors 132 a and 132 b,headlights, and the like. The voltage between the lead 208 and theground reference 210, which is a system voltage for the snowmobile 10,is essentially the same as the nominal voltage of the capacitance 145,although operating voltages between different system states may not beconstant at all times.

When the ICE 24 has been stopped for a long time, more than a few hoursfor example, the voltage on the capacitance 145 falls below the electricstart voltage threshold V_(MinE) and below the assisted start voltagethreshold V_(MinA), and the circuit 200 is not energized. Resorting tothe manual start procedure is therefore required for starting the ICE24. When the ICE 24 has been stopped for a relatively short time, aduration of which depends in large part on the energy storage capacityof the capacitance 145, the voltage on the capacitance 145 may be equalto or above the electric start voltage threshold V_(MinE), in which casethe electric start procedure is available. If the voltage of thecapacitance 145 is lower than the electric start voltage thresholdV_(MinE) while at least equal to or greater than the assisted startvoltage threshold V_(MinA), the assisted start procedure may beavailable. The assisted start procedure is described in more detailshereinbelow.

When the voltage of the capacitance 145 is at least equal or greaterthan the electric start voltage threshold V_(MinE), the user may depressthe electric start switch 168 (pushbutton) to invoke the electric startprocedure. This user action is sensed by a button state detector 212 ofthe ECU 164. The button state detector 212 being referenced to theterminal 206, it becomes placed in parallel with the capacitance 145when the start switch 168 is depressed. At the same time, electricalpower is provided from the capacitance 145 to the ECU 164, waking up theECU 164. Depending on specific implementations, the button statedetector 212 may accept a simple brief electrical contact provided bythe electric start switch 168 to initiate the electric start procedure.The button state detector 212 may alternatively require the electricstart switch 168 to be depressed for a few seconds. A variant in whichthe button state detector 212 is not present, in which the electricstart switch 168 needs to be depressed until the ICE 24 is actuallystarted is also contemplated. After sensing the electric start command,the button state detector 212 sends a signal to a wake up circuit 214 ofthe ECU 164. The wake up circuit 214 controls the following operations.

Initially, the wake up circuit 214 applies a signal to a driver 216 ofthe transistor Q1. The transistor Q1 turns on, effectively placing thecapacitance 145 in parallel with the capacitor C1. The wake up circuit214 can control the driver 216 to turn on and off the transistor Q1 at ahigh frequency in order to prevent excessive current flowing from thecapacitance 145 to the capacitor C1. Electrical conduction through thetransistor Q1 may be controlled in a small duty cycle at first, the dutycycle increasing as a voltage difference between the capacitor C1 andthe capacitance 145 decreases. Regardless, the capacitor C1 rapidlycharges to reach the voltage of the capacitance 145. The capacitance 145voltage may reduce slightly, but this effect is limited by the fact thatthe capacitor C1 is much smaller than the capacitance 145. After thecapacitor C1 has been charged, the electric start continues with the ECU164 controlling the delivery of power from the capacitance 145 to themotor-generator 144 via the lead 208, which is connected to the inverter146.

Once the electric start procedure has been successfully executed, asengine is running at idle, the motor-generator 144 may initially have alimited power generating capacity. Accessories of the snowmobile 10,including for example the fuel injectors 132 a and 132 b and headlights,require a certain amount of power. It is more critical to the operationof the vehicle to power these accessories than recharging thecapacitance 145. To avoid an excessive drop of the voltage of thecapacitor C1, at the lead 208, while the ICE 24 is idling, the ECU 164may optionally control the driver 216 to turn off the transistor Q1until the crankshaft 100 rotates at more than a predetermined revolutionthreshold. Once the ICE 24 has acquired a sufficient speed, the voltageat the lead 208 being now sufficient, the ECU 164 may again control thedriver 216 and the transistor Q1 to place the capacitance 145 inparallel with the capacitor C1. Once again, in order to avoid excessivecurrent flowing from the capacitor C1 to the capacitance 145 and toavoid an excessive voltage drop at the lead 208, the transistor Q1 maybe turned on and off at a small duty cycle at first, the duty cycleincreasing as a voltage difference between the capacitor C1 and thecapacitance 145 decreases. The transistor Q1 may therefore be controlledin order to regulate the charging rate of capacitance 145 whilerespecting the electrical power availability at any speed of the ICE 24.

The ECU 164 may optionally integrate an automatic shutdown circuit thatmay terminate all electrical functions of the snowmobile 10 in case ofsystem failure.

Table I provides a sequence of events including a manual start procedureof the ICE 24, followed by an electric start procedure command receivedafter a waiting time that does not exceed the capabilities of theelectric start system. In Table I, mentions of “PWM” refer to “pulsewidth modulation”, a technique used in the first and second controlstrategies as expressed hereinbelow.

TABLE I Motor- ECU 164 Capacitance Driver 216 generator TYPE Event stateC1 voltage 145 voltage duty cycle 144 MANUAL Initial OFF 0 volt 0 volt0% Stopped conditions Pulling Wake-Up Rising 0 volt 0% Rising the ropespeed (1^(st) time) Pulling Firing Rising to 0 volt 0% Rising to therope nominal idle speed (2^(nd) time) voltage Releasing Ignition/Nominal Rising, but less Partial to Idle speed the rope PWM voltage thannominal allow voltage charging of the capacitance Ready to Ignition/Nominal Rising, but less Partial to Slow apply PWM voltage than nominalallow charging throttle voltage charging of the capacitance Partial orIgnition/ Nominal Nominal 100%  Charging full PWM voltage voltagethrottle — Stop Turning Falling Nominal 0% Falling OFF voltage speedWaiting OFF Close to 0 Less than 0% Stopped time volt nominal voltage,but equal to or above V_(MinE) ELECTRIC Electric Wake-Up Close to 0 Lessthan 0% Stopped start volt nominal command voltage, but equal to orabove V_(MinE) — Ignition/ Equalizing to Reducing Partial to Stopped PWMthe slightly allow voltage capacitance equalization voltage — CrankingEqual to the Reducing, but 100%  Rising capacitance still equal to orspeed voltage above V_(MinR) — Firing Rising Rising 100%  Rising to idlespeed Ready to Ignition/ Nominal Nominal 100%  Idle speed apply PWMvoltage voltage throttle

In at least one implementation in which the fuel injectors 132 a and 132b are direct fuel injectors, both minimum voltage thresholds V_(MinE)and V_(MinR) may be defined within an operating voltage range of thedirect fuel injectors so that, if the voltage of the capacitance 145 isnot sufficient for the direct fuel injectors to inject fuel in thecylinders 106A, 106B, the electric start procedure is not attempted, orterminated if unsuccessful.

Electric Start Procedure

FIG. 9 is a logic diagram of a method for starting the engine of FIG. 2according to an implementation. A sequence shown in FIG. 9 comprises aplurality of operations, some of which may be executed in variableorder, some of the operations possibly being executed concurrently, andsome of the operations being optional. The method begins at operation300 when the ICE 24 of the snowmobile 10 is stopped. A voltage of thecapacitance 145 is measured by the voltage sensor 167 at operation 302.In the same operation 302, the display 186 may provide an “automaticstart” indication if the voltage meets or exceeds the electric startvoltage threshold V_(MinE) and if other conditions described hereinbelowfor the electric start procedure are met. The user actuates the electricstart switch 168, this being detected by the button state detector 212at operation 304. A comparison is made by the ECU 164, at operation 306,between the voltage of the capacitance 145 and the electric startvoltage threshold V_(MinE) to determine whether it is possible toinitiate the electric start procedure for the ICE 24. If it isdetermined that the voltage of the capacitance 145 is below the electricstart voltage threshold V_(MinE), the electric start procedure isprevented. Otherwise, verification is made at operation 308 that theengine temperature measured by the engine temperature sensor 172 meetsor exceeds an engine temperature threshold T₀. The electric startprocedure is prevented in this threshold for the engine temperature isnot met. Otherwise, verification is made at operation 310 that the ECUtemperature sensor 182 provides a reading of the temperature of the ECU164 that meets or exceeds an ECU temperature threshold T₁. The electricstart procedure is prevented if this threshold for the ECU temperatureis not met. Additional operations related to use of measurementsobtained from other sensors introduced in the foregoing description ofFIG. 6 may take place. These measurements may be provided to the ECU 164by the air temperature sensor 174, the atmospheric temperature sensor176, or the timer 180. Additional tests based on those measurements maybe executed by the ECU 164 to determine whether or not the electricstart procedure is likely to succeed or to determine a torque valuesufficient to cause the rotation of the crankshaft 100. For example, theelectric start procedure may be made conditional, in the ECU 164, on thetimer 180 informing the ECU 164 that a period of time since the ICE 24has been stopped is below a predetermined time value when the useractuates the electric start switch 168 at operation 304. On the basis ofthe period of time since the ICE 24 has been stopped, it is possible toestimate whether the voltage of the capacitance 145 will have fallenbelow the electric start voltage threshold V_(MinE) knowing a maximumcharge voltage of the capacitance 145 from a previous running sequenceof the ICE 24, and based on a typical energy leakage of the capacitance145.

Whether the electric start procedure is prevented because the voltage ofthe capacitance 145 is insufficient (operation 306), because the enginetemperature is too low (operation 308), because the ECU temperature istoo low (operation 310), or for any other reason, the method proceeds tooperation 312. At operation 312, the ECU 164 causes the display 186 todisplay “Manual Start” or some other message indicating to the user ofthe snowmobile 10 that the snowmobile 10 will need to be startedmanually using the recoil starter 156 (i.e. by pulling on the handle163). In implementations where the assisted start procedure isavailable, the display 186 may instead display “Assisted Start” or someother equivalent message, provided that current conditions allow usingthis procedure. Displaying the manual start indication or the assistedstart indication at operation 312 may follow any decision taken by theECU 164 to not proceed with the electric start procedure. It iscontemplated that instead of providing a message on the display 186,that the ECU 164 could cause a sound to be heard or provide some othertype of feedback to the user of the snowmobile 10, indicating that thesnowmobile 10 will need to be started manually using the recoil starter156. A manual start procedure or an assisted start procedure may beinitiated when the user pulls on the rope 158 of the recoil starter 156.If conditions for the assisted start procedure are met, this proceduremay be initiated as described hereinbelow. Otherwise, when theconditions for the assisted start procedure are not met, the manualstart procedure may be initiated at operation 314 when, in response tosensing the operation of the recoil starter 156 by the user of thesnowmobile 10, the ECU 164 initiates an engine control procedureassociated with the use of the recoil starter 156 in order to start theICE 24 using the recoil starter 156. Then at operation 316, the ECU 164determines if the ICE 24 has been successfully started using the recoilstarter 156. If not, then operation 314 is repeated. It is alsocontemplated that if at operation 316 it is determined that the ICE 24has not been successfully started, that the method could return tooperation 312 to display the message again. If at operation 316 it isdetermined that the ICE 24 has been successfully started, then themethod proceeds to operations 318 and 320, these last two (2) operationsbeing operated concurrently. At operation 318, the ECU 164 operates theICE 24 according to the control strategy or strategies to be used oncethe ICE 24 has started. At operation 320, the ECU 164 controls theinverter 146 to cause power to be delivered from the motor-generator 144to the capacitance 145, charging the capacitance 145 using the secondcontrol strategy at a voltage that remains fairly constant for a widerange of rotational speeds of the crankshaft 100. This may be achievedby the ECU 164 shunting one or more of the Phases A, B and C of themotor-generator 144 if, in the second control strategy, themotor-generator 144 generates a voltage that exceeds a maximum voltagethreshold. The ECU 164 may linearly regulate the voltage generated bythe motor-generator 144 may be using a series regulation mode or a shuntmode. The maximum voltage threshold may for example be equal or slightlysuperior to the nominal voltage of the circuit 200.

If at operations 306, 308 and 310 the ECU 164 determines that thecapacitance voltage is equal to or above the electric start voltagethreshold V_(MinE) and that the temperature conditions and any othercondition are also met, the method continues at operation 322 where theECU 164 controls the driver 216 of the transistor Q1 to place thecapacitance 145 in parallel with the capacitor C1 to equalize theirvoltages. Then at operation 324, the ECU 164 obtains a value of theangular position of the crankshaft 100 from the crankshaft positionsensor 170. This operation 324 may continue on an ongoing fashion duringthe complete electric start procedure so that the following operationsmay be optimized according to the varying angular position of thecrankshaft 100. It is contemplated that operations 322 and 324 may beomitted or substituted with other actions. For example, the electricstart procedure may be rendered independent from the angular position ofthe crankshaft 100 by providing a capacitance 145, the battery, or otherpower source having sufficient energy storage capability to rotate thecrankshaft 100 with no concern for its actual angular position.

The electric start procedure proceeds with operation 326 and continuesthrough operations 328, 330 and, if required, operation 332. Theseoperations are initiated in the sequence as shown on FIG. 9, but arethen executed concurrently until the electric start procedure is foundsuccessful or until it needs to be terminated.

At operation 326, the ECU 164 determines the torque value sufficient tocause the rotation of the crankshaft 100 and initiates delivery of powerfrom the capacitance 145 to the motor-generator 144, through theinverter 146, via the first control strategy which adapts the deliveryof power in view of the determined torque value. This transfer of powercauses a rotation of the crankshaft 100. Optionally, the ECU 164 maydetermine the torque value in sub-steps, in which a first sub-stepcomprises delivering electric power from the capacitance 145 to thethree-phase motor-generator 144 according to a first torque value tocause slow turning of the crankshaft at a first rotational speed untilthe piston is brought beyond its top dead center (TDC), based oninformation provided by the crankshaft position sensor 170 and based onthe contents of the control maps 166, a second sub-step comprisingdelivering electric power from the capacitance 145 to the three-phasemotor-generator 144 according to a second torque value, greater than thefirst torque value to cause turning of the crankshaft at a secondrotational speed, the second rotational speed being greater than thefirst rotational speed.

While operation 326 is ongoing, particularly while the second sub-stepis ongoing if operation 326 comprises two sub-steps, the method proceedsto operation 328 in which the ECU 164 causes the fuel injectors 132 a,132 b to inject fuel in the combustion chambers 132 a, 132 b and causesthe spark plugs 134 a, 134 b to ignite the fuel in the combustionchambers 134 a, 134 b, thereby accelerating the rotation of thecrankshaft 100. The angular position of the crankshaft 100 may be usedby the ECU 164 to properly time the fuel injection and the ignition. Ina particular implementation, the position sensor 170 is an absoluteposition sensor that can determine the position of the crankshaft 100while it is stationary, prior to starting of the ICE 140. This techniqueprovides precise fuel injection and ignition timing at a very lowrotational speed of the ICE 24, such as when the ICE 24 is starting.This technique decreases the chances of a failed start-up procedure dueto an insufficient combustion within the combustion chambers 120A, 120B,this insufficient combustion resulting from imprecise fuel injectionquantities or ignition timing calculated from an imprecise crankshaftposition. This technique further promotes faster synchronization betweenall components of the ICE 24 that rely on the position of the crankshaft100 when compared to the use of position sensors that require thecrankshaft 100 to be rotating to determine its position. Use ofmechanical actuators (not shown) operably connected to the crankshaft100 to control injection and ignition timings is also contemplated. Itis further contemplated that a quantity of fuel to be injected and theignition timing as applied by the ECU 164 at operation 328 may beevaluated using any known method, optionally depending on one or more ofan engine temperature, an air temperature, an atmospheric pressure, andan exhaust temperature, these values being provided to the ECU 164 bythe various sensors shown on FIG. 6.

While operations 326 and 328 are ongoing, the method proceeds tooperation 330, in which the ECU 164 compares a rotational speed of thecrankshaft 100 to a minimum revolution threshold to determine if the ICE24 has been successfully started using the electric start procedure. Ifthe rotational speed of the crankshaft 100 is equal to or above theminimum revolution threshold, the ICE 24 has been successfully started,the electric start procedure ends and the method proceeds to operations318 and 320, which are described hereinabove.

If, at operation 330, the ECU 164 determines that the ICE 24 has not yetbeen started, the rotational speed of the crankshaft 100 being below theminimum revolution threshold, the method continues at operation 332where the ECU 164 monitors again the voltage of the capacitance 145. Itis expected that this voltage will be reduced somewhat as energypreviously stored in the capacitance 145 has been spent duringoperations 326 and 328. However, if a remaining voltage of thecapacitance 145 is equal to or above the residual voltage thresholdV_(MinR), the electric start procedure returns to operations 326 and328, which are still ongoing, and then at operation 330. If however theECU 164 determines at operation 332 that the capacitance voltage hasfallen below the residual voltage threshold V_(MinR), the methodproceeds to operation 334 where the ECU 164 ceases the delivery of powerfrom the capacitance 145 to the motor-generator 144 and terminatesoperations 326 and 328. The method then moves from operation 334 tooperation 312, which is described hereinabove, in which the ECU 164causes the display 186 to display a manual start indication, or anassisted start indication in implementations where this option isavailable, operation 312 being followed by operations 314, 316, 318 and320 in the case of a manual start.

FIG. 10 is a timing diagram showing an example of variations of anengine resistive torque as a function of time along with correspondingengine rotational speed variations. A graph 400 shows a variation of theresistive torque of the ICE 24, in Newton-Meters (Nm) as a function oftime, in seconds. The graph 400 was obtained from a Simulink™ model. Agraph 402 shows a corresponding variation of a rotational speed of thecrankshaft 100 over the same time scale. In the simulation, thetwo-cylinder ICE 24 is firing when a piston first reaches near TDC.After less than 0.1 seconds, the resistive torque becomes negativebecause the piston has passed beyond its TDC. Compression present in thecombustion chamber pushes on the piston and accelerates the rotation ofthe crankshaft 100. At about 0.12 seconds, the ECU 164 controls thetorque applied to the crankshaft 100 by the motor-generator 144,accelerating the rotation of the crankshaft 100. The rotational speed ofthe crankshaft 100 reaches a plateau at about 0.17 seconds because thepiston is now compressing gases present in the combustion chamber. Therotational speed decreases as the piston arrives near its TDC. TDC isreached at about 0.32 seconds. Successful ignition takes place,whereafter the rotational speed of the crankshaft 100 increases rapidlywhile the resistive torque on the motor-generator 144 becomesessentially negative, following a toothed saw wave shape as the pistoncycles up and down in its cylinder.

Assisted Start Procedure

FIG. 11 is a logic diagram of a method for starting the engine of FIG. 2according to another implementation. A sequence shown in FIG. 11comprises a plurality of operations, some of which may be executed invariable order, some of the operations possibly being executedconcurrently, and some of the operations being optional. The methodbegins at operation 600 when the ICE 24 of the snowmobile 10 is stopped.A voltage of the capacitance 145 is measured by the voltage sensor 167at operation 602. In the same operation 602, the display 186 may providean “assisted start” indication if the voltage meets or exceeds theassisted start voltage threshold V_(MinA) and if other conditionsdescribed hereinbelow for the assisted start procedure are met. Atoperation 604, the user initiates a rotation of the crankshaft 100 bypulling on the rope 158 of the recoil starter 156. At operation 606, thecrankshaft position sensor 170 detects an initial rotation of thecrankshaft 100 and informs the ECU 164 of the rotation. Detecting theinitial rotation of the crankshaft 100 may be conditional to thecrankshaft position sensor 170 detecting that a revolution speed of thecrankshaft 100 meets or exceeds a minimal revolution threshold. Acomparison is made by the ECU 164 at operation 608 between the voltageof the capacitance 145 and the assisted start voltage threshold V_(MinA)to determine whether it is possible to initiate the assisted startprocedure for the ICE 24. If it is determined that the voltage of thecapacitance 145 is below the assisted start voltage threshold V_(MinA),the assisted start procedure is prevented. Otherwise, verification ismade at operation 610 that the engine temperature measured by the enginetemperature sensor 172 meets or exceeds an engine temperature thresholdT₀. The assisted start procedure is prevented in this threshold for theengine temperature is not met. Otherwise, verification is made atoperation 612 that the ECU temperature sensor 182 provides a reading ofthe temperature of the ECU 164 that meets or exceeds an ECU temperaturethreshold T₁. The assisted start procedure is prevented if thisthreshold for the ECU temperature is not met. Additional operationsrelated to the use of measurements obtained from other sensorsintroduced in the foregoing description of FIG. 6 may take place. Thesemeasurements may be provided to the ECU 164 by the air temperaturesensor 174, the atmospheric temperature sensor 176, or the timer 180.Additional tests based on those measurements may be executed by the ECU164 to determine whether or not the assisted start procedure is likelyto succeed. For example, the assisted start procedure may be madeconditional, in the ECU 164, on the timer 180 informing the ECU 164 thata period of time since the ICE 24 has been stopped is below apredetermined time value when the user pulls on the rope 158 of therecoil starter 156 at operation 604, On the basis of the period of timesince the ICE 24 has been stopped, it is possible to estimate whetherthe voltage of the capacitance 145 will have fallen below the assistedstart voltage threshold V_(MinA) knowing a maximum charge voltage of thecapacitance 145 from a previous running sequence of the ICE 24, andbased on a typical energy leakage of the capacitance 145.

Displaying the manual start indication at operation 614 may follow anydecision taken by the ECU 164 to not proceed with the assisted startprocedure. Whether the assisted start procedure is prevented because thevoltage of the capacitance 145 is insufficient (operation 608), becausethe engine temperature is too low (operation 610), because the ECUtemperature is too low (operation 612) or for any other reason, themethod proceeds to operation 614. At operation 614, the display 186 maydisplay “Manual Start”. Following operation 614, the user may continuepulling on the rope 158 of the recoil starter 156 at operation 616.Operation 616 may continue until it is detected at operation 618 thatthe ICE 24 is properly started. Control of ICE 24 and delivery ofelectric power from the motor-generator 144 to the capacitance 145follow at 620 and 622, which are the same or equivalent as operations318 and 320 of FIG. 9 including, in an implementation, controlling theICE 24 using the above described control strategies.

If at operations 608, 610 and 612, the ECU 164 determines that thecapacitance voltage is equal to or above the assisted start voltagethreshold V_(MinA) and that the temperature conditions and any furthercondition are also met, the method continues at operation 624 where theECU 164 controls the driver 216 of the transistor Q1 to place thecapacitance 145 in parallel with the capacitor C1 to equalize theirvoltages.

The assisted start procedure proceeds with operation 626 and continuesthrough operations 628, 630 and, if required, operation 632. Theseoperations are initiated in the sequence as shown on FIG. 11, but arethen executed concurrently until the assisted start procedure is foundsuccessful or until it needs to be terminated.

At operation 626, the ECU 164 initiates delivery of power from thecapacitance 145 to the motor-generator 144, through the inverter 146.This transfer of power accelerates the rotation of the crankshaft 100and reduces the amount of effort that needs to be exerted by the userpulling on the rope 158 of the recoil starter 156. The ECU 164 mayoptionally determine a torque value in the same manner as described inthe foregoing description of operation 326 (FIG. 9).

While operation 626 is ongoing, the method proceeds to operation 628 inwhich the ECU 164 causes the fuel injectors 132 a, 132 b to inject fuelin the combustion chambers 132 a, 132 b and causes the spark plugs 134a, 134 b to ignite the fuel in the combustion chambers 134 a, 134 b,thereby accelerating further the rotation of the crankshaft 100. Theangular position of the crankshaft 100 may be used by the ECU 164 toproperly time the fuel injection and the ignition. Use of mechanicalactuators (not shown) operably connected to the crankshaft 100 tocontrol injection and ignition timings is also contemplated. It isfurther contemplated that a quantity of fuel to be injected and theignition timing as applied by the ECU 164 at operation 628 may depend onone or more of an engine temperature, an air temperature, an atmosphericpressure, and an exhaust temperature, these values being provided to theECU 164 by the various sensors shown on FIG. 6.

While 626 and 628 are ongoing, the method proceeds to operation 630, inwhich the ECU 164 compares a rotational speed of the crankshaft 100 to aminimum revolution threshold to determine if the ICE 24 has beensuccessfully started using the assisted start procedure. If therotational speed of the crankshaft 100 is equal to or above the minimumrevolution threshold, the ICE 24 has been successfully started, theassisted start procedure ends and the method proceeds to 620 and 622,which are described hereinabove.

If, at operation 630, the ECU 164 determines that the ICE 24 has not yetbeen started, the rotational speed of the crankshaft 100 being below theminimum revolution threshold, the method continues at operation 632where the ECU 164 monitors again the voltage of the capacitance 145. Itis expected that this voltage will be reduced somewhat as energypreviously stored in the capacitance 145 has been spent during 626 and628. However, if a remaining voltage of the capacitance 145 is equal toor above a residual voltage threshold, the assisted start procedurereturns to operations 626 and 628, which are still ongoing, and then atoperation 630. In one variant, the residual voltage threshold applicableto the assisted start procedure may be the same value V_(MinR) as in thecase of the electric start procedure. In another variant, a differentresidual voltage threshold may be used given that the amount of powerdelivered to the motor-generator 144 by the capacitance 145 complementsthe effort of the user pulling on the rope 158 of the recoil starter156. If however the ECU 164 determines at operation 632 that thecapacitance voltage has fallen below the residual voltage thresholdV_(MinR), the method proceeds to operation 634 where the ECU 164 ceasesthe delivery of power from the capacitance 145 to the motor-generator144 and terminates operations 626 and 628. The method then moves fromoperation 634 to operation 614, which is described hereinabove, in whichthe ECU 164 causes the display 186 to display a manual start indication,operation 614 being followed by operations 616, 618, 620 and 622.

In an implementation, the snowmobile 10 may be configured to support anyone of the manual, electric and assisted start procedures. In suchimplementation, operation 312 (FIG. 9) may provide a manual start or anassisted start indication, depending on the voltage of the capacitance145. If the voltage of the capacitance is below the electric startvoltage threshold V_(MinE) while meeting or exceeding the assisted startvoltage threshold V_(MinA), operation 312 of FIG. 9 may provide theassisted start indication and may be followed by operation 604 of FIG.11 if the user pulls on the rope 158 of the recoil starter 156. Also inthis implementation, after having started the ICE 24 using the assistedstart procedure, the ICE 24 may be stopped and the display 186 mayprovide an indication of the available start procedure depending oncurrent conditions reported to the ECU 164 by the various sensors.

Implementations of the Control Strategies

As expressed hereinabove, the ECU 164 controls the inverter 146 throughthe strategy switch 184. To this end, the ECU 164 generates controlpulses that are applied to the strategy switch 184. These control pulsesare generated differently in the two (2) control strategies. In at leastone implementation, the effect of these control pulses depends on theinternal structure of the inverter 144. FIG. 12 is a circuit diagramshowing connections of the inverter 146, the capacitance 145 and themotor-generator 144 of FIG. 6. As shown on FIG. 12, the inverter 146 hasthree phases, each phase being electrically connected to a correspondingphase of the three-phase motor-generator 144. In more details, theinverter 146 is formed of three (3) switching legs, each switching legincluding a pair of MOSFETs T1, T2, T3, T4, T5 and T6 matched withcorresponding freewheel diodes D2, D1, D3, D2, D6 and D5. For instance,a first leg forming a first phase includes a top transistor T1 matchedwith a freewheel diode D2 and a bottom transistor T2 matched with afreewheel diode D1. A second leg forming a second phase includestransistors T3 and T4 matched with diodes D4 and D3 respectively while athird leg forming a third phase includes transistors T5 and T6 matchedwith diodes D6 and D5 respectively. As substitutes to MOSFETs, bipolartransistors, for example IGBTs, or any other power electronic switchesare also contemplated. Each transistor T1-T6 has a corresponding gateG1-G6 through which a signal, or control pulse, can be applied under thecontrol of the ECU 164 via the strategy switch 184, either directly orthrough a gate driver (not shown), to turn-on (short-circuit) orturn-off (open circuit) the corresponding transistors T1-T6. Thefreewheel diodes D1-D6 are used to attenuate transient overvoltage thatoccurs upon switching on and off of the transistors T1-T6.

For example, when the motor-generator 144 is in motor operating mode,being used as a starter for the ICE 24, a first control pulse is appliedat the gate G1 to short-circuit the transistor T1. Current flows from apositive tab of the capacitance 145 through the transistor T1 andreaches a phase of the motor-generator 144 defined between an input Aand a neutral connection between the phases of the motor-generator 144,hereinafter “Phase A”. Thereafter, the first control pulse is removedfrom the gate G1 so the transistor T1 becomes an open-circuit. At thesame time, a second control pulse is applied on the gate G2, causing thetransistor T2 to turn-on. Current now flows in the opposite direction inPhase A of the motor-generator 144, returning to a negative tab of thecapacitance 145 via the transistor T2. As a result of this sequence ofturning on and off the transistors T1 and T2, an alternating currentflows in the Phase A of the motor-generator 144.

The current flowing into Phase A of the motor-generator 144 needs toexit through one or both of the other phases of the motor-generator 144.“Phase B” is defined between an input B and the neutral connection.“Phase C” is defined between an input C and the neutral connection. Thecurrent flows from Phase A through Phase B, or Phase C, or both Phases Band C, depending on whether one or both of transistors T4 or T6 isturned on by control pulses applied on their respective gates G4 or G6when the transistor T1 is also turned on. The current exiting themotor-generator 144 via one or both of Phases B and/or C returns to anegative tab of the capacitance 145 through one or both of thetransistors T4 and/or T6. The freewheel diodes D1-D6 assist insupporting phase inductance currents during freewheel periods.

To operate the motor-generator 144 as a conventional three-phase motor,current would flow concurrently in all three (3) Phases A, B and C, atiming control of the various transistors T1-T6 being separated by 120degrees. Other operating modes of the motor-generator 144 in whichcurrent does not concurrently flow in all three (3) Phases A, B and Care however contemplated.

Examples of parameters that may be considered by programming of the ECU164 to control the delivery of electric power in both control strategiesinclude, without limitation, current and voltage of each phase voltagesand currents in each of the Phases A, B and C of the motor-generator144, the angular position and rotational speed of the crankshaft 100.The ECU 164 uses these values to determine an electromagnetic torque ofthe motor-generator 144, this torque having positive value when themotor-generator 144 is used during the electric start procedure or theassisted start procedure and a negative value when used in generatoroperating mode.

The first control strategy uses a technique called vector control orfield-oriented control (FOC). The first control strategy is used mainlyto control the delivery of electric power from the capacitance 145 tothe motor-generator 144 to cause or assist a rotation of the crankshaft100 in the electric start procedure or in the assisted start procedureof the ICE 24. In one implementation, ECU 164 determines a torquerequest sufficient to cause the rotation of the crankshaft 100. Inanother implementation, the ECU 164 determines a speed requestapplicable to the crankshaft 100, sufficient to cause ignition and startof the ICE 24. This determination of the speed request or torque requestmay be made by the ECU 164 applying a predetermined speed or torquerequest value or pattern based on the contents of the control maps 166.The ECU 164 may increment the torque request if a first torqueapplication causes no rotation of the crankshaft 100. The ECU 164 mayincrement the speed request if a rotation of the crankshaft 100 is notsufficient to allow ignition and start of the ICE 24. Alternatively, theECU 164 may calculate the speed or torque request based on a combinationof parameters, including in a non-limitative example a mathematicalrepresentation of internal components of the ICE 24 and on the angularposition of the crankshaft 100. The ECU 164 controls the delivery ofelectric power from the capacitance 145 to the motor-generator 144,based on the determined speed request or torque request, through thegeneration of control pulses applied to selected ones of the transistorsT1-T6. Using vector control, the ECU 164 calculates a number, timing,and width of the various control pulses so that the amount of electricpower flowing from the capacitance 145 through the inverter 146 and tothe motor-generator 144 fulfills the determined speed or torque request.This manner of controlling the transistors T1-T6 by applying timedpulses to their gates G1-G6, each pulse having a calculated width, isknown as pulse width modulation (PWM).

FIG. 13 is a block diagram of a typical implementation of a vectorcontrol drive. A vector control drive 500 of FIG. 13 may be implementedat least in part in the ECU 164. An input to the vector control driveincludes a set point 504 for a required speed (the speed request) thatis determined as sufficient for starting the ICE 24. This set point 504is applied to a slow speed control loop 506. Other inputs to the vectorcontrol drive 500 include current measurements 508 _(a), 508 _(b) and508 _(c) for the three phases of the motor-generator 144 and a voltagemeasurement 510 obtained from the inverter 146 and/or from themotor-generator 144. These current and voltage measurements are appliedto an analog to digital converter (ADC) 512. Crankshaft angular positionmeasurements (encoder signals u_(A), u_(S)) 514 are applied to aquadrature timer 516. The quadrature timer 516 calculates an actualposition of the crankshaft 100. The ADC 512 calculates a digitizedvoltage value 518 and digitized current values 520 _(a), 520 _(b) and520 _(c) for the three phases of the motor-generator 144. Thesedigitized values and an actual position 522 of the crankshaft 100calculated by the quadrature timer 516 are provided to a fast currentcontrol loop 524. The actual position 522 of the crankshaft 100 isconverted to an actual (measured) speed 526 by a speed calculator 528 ofthe slow speed control loop 506. A difference 528 between the measuredspeed 526 and the required speed set point 504 is applied to a firstproportional-integral (PI) controller 530 that in turn yields acurrent-image 532 of a torque request that is applied as a set point(Isq_req) to the fast current control loop 524.

As expressed hereinabove, in some variants, it may be desired to operatethe motor-generator 144 so that it delivers electric power to thecapacitance 145 in the first control strategy, at least at lowrevolution speeds of the crankshaft 100. To this end, an optional fieldweakening module 534 having an internal map attenuates values of itsoutput based on the measured speed 526 of the crankshaft 100 to providea current-image 536 of a magnetic field of the motor-generator 144 as anadditional set point (Isd_req) applied to the fast current control loop524.

In the fast current control loop 524, a Clark Transform 538 converts thethree-phase current measurements 520 _(a), 520 _(b) and 520 _(c) into atwo-phase model 540. A Park Transform 542 fed with sine and cosinevalues 523 of the actual position 522 of the crankshaft 100, calculatedby a sin/cos converter 525, converts further this model 540 to provide astationary current-image 544 of the actual torque on the motor-generator144 (Isq) and a stationary current-image 546 of the actual magneticfield of the motor-generator (Isd). Outputs 544 and 546 of this modelare respectively compared to the Isq_req set point 532 and to theIsd_req set point 536 (if used), and their differences are respectivelyapplied to second and third PI controllers 548, 550. An Inverse ParkTransform 552 is applied to stationary voltage requests Uq 554 and Ud556 produced by the second and third PI controllers 548, 550, theInverse Park Transform 552 using the sine and cosine values 523 of theactual position 522 of the crankshaft 100 to produce outputs 558, 560 ofthe Inverse Park Transform 552 that are applied to a space vectormodulation-pulse width modulation (SV-PWM) transform 562. In turn, theSV-PWM transform 562 provides three-phase control 564 to a PWM module566 that generates pulses 502 that the ECU 164 provides for applicationto the gates G1-G6 of the inverter 146.

The ECU 164 may control a delivery of electric power from thecapacitance 145 to the motor-generator 144 based on a pre-determinedamount of torque, or torque request, sufficient to cause rotation of thecrankshaft 100 for starting the ICE 24. However, considering that theamount of torque required to rotate the crankshaft 100 before ignitionof the cylinder (or cylinders) varies based on the angular position ofthe crankshaft 100 in relation to the top dead center (TDC) position ofeach piston, calculation of a variable torque request is alsocontemplated. In a variant, the angular position of the crankshaft 100is provided by the crankshaft position sensor 170 or, alternatively, bya relative position sensor. When using the relative position sensor, ateach operational sequence of the ECU 164, prior to initiating rotationof the crankshaft 100, the ECU 164 magnetizes two out of the threephases of the alternating current motor-generator 144, moving and thenlocking the rotor of the motor-generator 144 and thereby locking thecrankshaft 100, which is attached thereto, in a known repetitiveelectric angle. From there, rotating positions of the crankshaft 100 arecalculated continuously from a counter of pulses received from therelative position sensor. An absolute position of the crankshaft 100 iscalculated and an electric angle is derived from that calculation toperform vector control. In a particular implementation, an incrementalencoder providing 1024 pulses per revolution of the crankshaft 100 iscontemplated. Sensorless control of the crankshaft position is alsopossible, though with this solution, producing high torque at very lowangular velocity of the crankshaft 100 may be rather challenging.Regardless, in a variant introduced in the foregoing description ofoperation 326 (FIG. 9), the ECU 164 calculates or otherwise determinesthe torque request based on an angular position of the crankshaft 100provided by the crankshaft position sensor 170, values of the torquerequest being updated at various points of the rotation of thecrankshaft 100. As a result, the torque request can be optimized so thatit is sufficient to rotate the crankshaft 100 as it reaches variousangular positions while using as little as possible of the energy storedin the capacitance 145. In a particular variant, the ECU 164 controlsthe amount of torque applied on the motor-generator 144 so that it turnsat a very low speed until a given piston 116A, 116B passes its TDC for afirst time. During this brief period of time, gas is slowly expelledfrom the combustion chamber 120A, 120B in which this given piston 116A,116B is located. Very little energy is drawn from the capacitance 145 inthis operation. Once the piston 116A, 116B has moved beyond its TDC, thecrankshaft 100 has acquired at least some momentum. The ECU 164 thenraises the torque request applied to the motor-generator 144 so that thecrankshaft 100 rotates at a speed sufficient to allow injection of fuelin the combustion chamber 120A, 120B as the piston 116A, 116B movestowards its TDC, ignition taking place in the combustion chamber 120A,120B as soon as the piston moves beyond its TDC. This increase of thetorque request may be linear until a predetermined torque set-point isreached, so that the rotational speed of the crankshaft 100 increasessmoothly.

Following starting of the ICE 24, irrespective of whether the ICE 24 wasstarted using the manual start procedure, the assisted start procedureor the electric start procedure, the crankshaft 100 drives themotor-generator 144 at a variable rotational speed, most of the timesignificantly exceeding a rotational speed used in the course of any ofthe start procedures. Once the ICE 24 is started, operation of themotor-generator 144 switches to generator operating mode. In animplementation, the ECU 164 may determine a revolution speed of thecrankshaft 100 based on successive readings provided by the crankshaftposition sensor 170 and cause the motor-generator 144 to startdelivering electric power to the capacitance 145 when the revolutionspeed of the crankshaft meets or exceeds a minimal revolution threshold.At this point or soon thereafter, the ECU 164 starts controlling thestrategy switch 184 and the inverter 146 using the second controlstrategy. Optionally, the first control strategy may be used ingenerator operating mode until the voltage measurement provided by thevoltage sensor 167 meets or exceeds a voltage generation threshold. Thevoltage generation threshold can be set slightly lower than a nominalvoltage of the capacitance 145, for example.

The second control strategy uses a “shunt” technique. The output of themotor-generator 144, now generating, is used to charge the capacitance145, to supply electrical power to the injectors 132 a, 132 b, to sparkthe spark plugs 134 a, 134 b, and, generally, to supply electrical powerto electrical accessories of the snowmobile 10. To this end, the ECU 164alters a position of the strategy switch 184 so that electrical powernow flows from the motor-generator 144 to the capacitance 145, stillthrough the inverter 146. The ECU 164 monitors the voltage of thecapacitance 145 through measurements obtained from the voltage sensor167. Based on these voltage measurements, the ECU 164 generates controlpulses that are applied, via the strategy switch 184, to the gates G1-G6of the transistors T1-T6 in the inverter 146. PWM is still applied bythe ECU 164 to the gates G1-G6, but this time according to the secondcontrol strategy.

If an output voltage of the motor-generator 144 is above its nominalvalue, or above its nominal value plus a predetermined tolerance factor,the inverter 146 is controlled by the ECU 164 to reduce the voltage atwhich electrical power is delivered from the motor-generator 144 to thecapacitance 145. To this end, in one operating dissipative voltageregulation mode, the ECU 164 may generate control pulses applied tovarious gates G2, G4 and G6 to effectively bypass, or “shunt”, one ormore of the phases of the motor-generator 144, at the same time applyingno control pulse to the gates G1, G3 and G5 in order to cause thetransistors T1, T3 and T5 to remain non-conductive (open circuit). Forexample, applying pulses to the gates G2 and G6 causes the transistorsT2 and T6 to turn on and become conductive. As a result, a closed loopis formed between Phases A and C of the motor-generator 144 along withthe transistors T2 and T6. Under this condition, no electrical power isdelivered from two (2) of the phases of the motor-generator 144 to thecapacitance 145. A duration (width) and timing of the pulses applied tothe gates G2 and G6 impacts a duration of time when Phases A and C areshunted, in turn impacting the charging voltage applied at thecapacitance 145. PWM can be applied to any pair of the bottomtransistors T2, T4 and T6, so that they can be shorted at a desired timeto shunt a pair of phases of the motor-generator 144. The ECU 164 mayactually modify, over time, a determination of which pair of transistorsis made part of a shunt in order to avoid their overheating due toconduction losses in the inverter 146. To this end, voltage regulationin shunt mode involves successively activating the transistors T2, T4and T6. As a result, the delivery of electric power from themotor-generator 144 to the capacitance 145 can be made at a desiredvoltage over a broad range of the rotational speed of the crankshaft100. A series voltage regulation mode is also contemplated, in which thefreewheel diodes D1, D3 and D5 may optionally be replaced by additionaltransistors (not shown) mounted in reverse-parallel with the transistorsT1, T3 and T5, these additional transistors being turned on and off asrequired to allow current from the motor-generator 144 to recharge thecapacitance 145 while not exceeding the nominal voltage value.

In a particular implementation, voltage regulation in shunt mode maybenefit from the measurements provided by the position sensor 170. Inthis implementation, the position sensor 170 allows the ECU 164 todetermine a mechanical position of the crankshaft 100. The ECU 164calculates an equivalent electrical angle by multiplying the mechanicalposition of the crankshaft 100 by a known number of pole pairs of themotor-generator 144. If the output voltage of the motor-generator 144 isabove a predetermined value, starting from a voltage rise of any one ofthe phases A, B or C, all three (3) phases are consecutively shuntedonce, in synchrony with the operation of the motor-generator 144. Thisshunting sequence may be repeated when the output voltage of themotor-generator 144 rises again above the predetermined value.

If the voltage of the capacitance 145 is at or below its nominal value,the inverter 146 is controlled by the ECU 164 to deliver electricalpower available from the motor-generator 144 to the capacitance 145without shunting any of the Phases A, B or C. Under this condition,which may for example occur for a brief duration after the start of theICE 24, the control of the power delivery could be construed as aneutral control mode distinct from the first and second controlstrategies. In the neutral control mode, the inverter 146 acts as athree-phase full-wave diode bridge rectifier, providing no voltage orcurrent regulation.

FIG. 14 is a block diagram of an electric system according to animplementation of the present technology. A circuit 700 includesvariants of elements introduced in the foregoing description of thevarious drawings, these elements being grouped into subsystems. Themotor-generator 144 is one such subsystem. Another subsystem is in theform of a control module 702 that, in an implementation, comprises asingle physical module including a processor 703 programmed to executethe functions of the ECU 164, the inverter 146, the ECU temperaturesensor 182 and further includes a DC-DC converter 704. As shown, the ECU164 includes connections for the electric start switch 168, for themeasurements provided by the various sensors 170, 172, 174, 176 and 182,and connections to the gates G1-G6 of the inverter 146. In theillustrated example, the voltage sensor 167 is implemented as a DCvoltage sensor 167 _(DC) that measures a voltage of the capacitance 145and as an AC voltage sensor 167 _(AC) that measures a voltage on onephase of the motor-generator 144, these two components of the voltagesensor 167 being integrated within the ECU 164. Use of external voltagesensors operatively connected to the ECU 164 is also contemplated. Athird subsystem 706 includes the capacitance 145, as well as a chargingcircuit 705 and a discharging circuit 707 that use the driver 216 andthe transistor Q1 of FIG. 8 to control charging and discharging of thecapacitance 145.

The circuit 700 operates at a nominal system voltage, which is typicallythe voltage of the capacitance 145 when fully charged. A fourthsubsystem 708 includes components of the snowmobile 10 that operate atthe system voltage. These components may include the fuel injectors 132a, 132 b, an electric oil pump 710, ignition coils 712 for the sparkplugs 134 a, 134 b and a fuel pump 714. A fifth subsystem 716 includesaccessories of the snowmobile 10 that operate at an accessory voltage.These accessories may include a multi-port fuel injector (MPH) 718,lighting 720, an instrument cluster 722 including the display 186,heated grips 724 mounted on the handlebar 36 and an exhaust valve 726.The DC-DC convertor 704 converts the system voltage to the accessoryvoltage and thus provides electric power to the accessories.

In an implementation, the circuit 700 normally operates at a systemvoltage of 55 volts and some accessories of the snowmobile normallyoperate at an accessory voltage of 12 volts. In this implementation, theDC-DC converter 704 is a 55V-12V converter. These values for the systemvoltage and for the accessory voltage are nominal for thisimplementation and may vary according to the actual operating conditionsof the snowmobile 10.

FIG. 15 is a timing diagram showing an example of a sequence forchanging the control strategy for the delivery of electric power betweenthe capacitance 145 and the motor-generator 144 along with correspondingengine rotational speed variations. A graph 410 shows a variation ofelectrical power delivery control strategies applied by the ECU 164, asa function of time, in seconds. In this graph 410, “Strategy 1”indicates the application of the first control strategy, specificallyusing a vector control, “Strategy 2” indicates the application of thesecond control strategy, which uses shunting of phases of themotor-generator 144 to control the voltage applied to charge thecapacitance 145, and “Neutral” indicates the application of the neutralcontrol mode. In the neutral control mode, the voltage generated by themotor-generator 144 may simply be converted to direct current andapplied to charge the capacitance 145, provided that a peak backelectromotive force voltage of the motor-generator 144 is higher thanthe nominal voltage of the circuit 200, a condition that is usually metwhen the ICE 24 reaches a sufficient revolution speed. A graph 412 showsa corresponding variation of a rotational speed of the crankshaft 100over a same time scale. In a first half-second of operation followingthe user command for the electric start procedure for the ICE 24, nopower is delivered between the capacitance 145 and the motor-generator144. This period is used to equalize the voltages of the capacitance 145and of the capacitor C1. The actual duration of this period may varyconsiderably as a function of the value of the capacitor C1. A periodranging from 0.5 to about 1.1 seconds corresponds essentially to theperiod covered between 0 and 0.4 seconds on the graphs 400 and 402. TheECU 164 uses the first control strategy (Strategy 1) to control deliveryof electric power from the capacitance 145 to the motor-generator 144until the ICE 24 is actually started. Then, between 1.1 and 1.3 seconds,as the ICE 24 accelerates, electric power is delivered from themotor-generator 144 to the capacitance 145 in the neutral control mode.When the crankshaft 100 reaches a sufficient rotational speed, at about1.3 seconds, the motor-generator 144 starts generating power at avoltage that tends to exceed the nominal voltage of the capacitance 145.This is when the ECU 164 starts using the second control strategy(Strategy 2) to control delivery of electrical power from themotor-generator 144 to the capacitance 145. A variant in which theneutral control mode is not implemented is also contemplated, in whichthe ECU 164 starts using the second control strategy as soon as the ICE24 is successfully started.

FIG. 16 is another timing diagram showing an example of an impact of thecontrol strategies on a current exchanged between the capacitance andthe ETM and on system voltage. A graph 420 shows a voltage of one of thePhases A, B or C of the motor-generator 144 as a function of time, inseconds, and as a function of the control strategies. In the firstcontrol strategy, the ECU 164 controls the application of voltage pulsesto the motor-generator 144 in pulse width modulation (PWM) mode, at avery rapid rate typically expressed in kilohertz. Then, as ignition ofthe ICE 24 beings, in the neutral control mode, the motor-generator 144starts generating voltage on its own, this voltage increasing until themode changes to the second control strategy, the voltage cycling at arate that follows the rotation of the crankshaft 100. It may be observedthat because of the configuration of the inverter 146, the voltage oneach phase of the motor-generator alternates between zero (0) volt andthe nominal system voltage without cycling through negative values. Agraph 422 shows a variation of a current flowing between the capacitance145 and the motor-generator 144 as the ECU 164 changes from the firstcontrol strategy to the neutral control mode to the second controlstrategy. Initially, in the first control strategy, a three-phasecurrent flows from the capacitance 145 toward the motor-generator 144,through the inverter 146. For most of the neutral control strategy, alltransistors T1-T6 of the inverter are open and no current flows betweenthe capacitance 145 and the motor-generator 144. Significant current isgenerated by each phase of the motor-generator 144 after the start ofthe ICE 24. The ECU 164 applies shunting of the phases of themotor-generator 144 for preventing excess voltage at its output, asillustrated by the strong variations of the current in the right-handpart of graph 422. The graph 424 shows an actual voltage measured on thecapacitance 145 as the ECU 164 changes from the first control strategyto the neutral control mode to the second control strategy. The voltageof the capacitance 145 initially decreases while electric power isdelivered to the motor-generator 144. Following ignition of the ICE 24,the ECU 164 places the system in neutral control mode. A discharge ofthe freewheel diodes D1-D6 causes a modest increase of the voltage ofthe capacitance 145. Opening of the transistor Q1 at the beginning ofthe operation in the second control strategy temporary isolates thecapacitance 145 from the motor-generator so that electric power producedby the motor-generator 144 is mainly available for other needs of thesystem, such as injection, ignition, control, and the like. Closingagain of the transistor Q1 allows charging of the capacitance 145, witha voltage that oscillates near the nominal system voltage according tothe shunting of the motor-generator 144.

The timing values, rotational speed values, and torque valuesillustrated in the various graphs 400, 402, 410, 412, 420, 422 and 424are provided for illustration and do not limit the present disclosure.Actual values may depend greatly on the construction of the ICE 24, ofthe motor-generator 144, of the capacitance 145 and on the operationstrategy of the ECU 164.

Modifications and improvements to the above-described implementations ofthe present technology may become apparent to those skilled in the art.For example, it is contemplated that the ICE 24 could be provided with adecompression system. The decompression system can release pressure inthe combustion chambers 120A, 120B, thereby reducing compression forcesthat need to be overcome by the motor-generator 144 at operations 326and 626 described above. Therefore, by providing a decompression system,it is contemplated that the motor-generator 144 could be even smallerand lighter, a size and a weight of the capacitance 145 being reducedaccordingly. The foregoing description is intended to be exemplaryrather than limiting. The scope of the present technology is thereforeintended to be limited solely by the scope of the appended claims.

What is claimed is:
 1. A method for operating an electric turningmachine (ETM) operatively connected to an internal combustion engine,the method comprising: operating the ETM as a motor with a first controlstrategy to increase a rotational speed of the internal combustionengine up to at least a minimum revolution threshold, operating with thefirst control strategy comprising delivering electric power from a powersource to the ETM selectively through at least one transistor of anelectrical converter; switching from the first control strategy to asecond control strategy in response to the rotational speed of theinternal combustion engine being equal to or above the minimumrevolution threshold, the second control strategy being distinct fromthe first control strategy; and in response to switching from the firstcontrol strategy to the second control strategy, operating the ETM as agenerator with the second control strategy, operating with the secondcontrol strategy comprising delivering electric power from the ETM to anaccessory selectively through the at least one transistor of theelectrical converter.
 2. The method of claim 1, further comprisingswitching from the first control strategy to the second control strategyin response to a voltage of the ETM being equal to or above a voltagegeneration threshold.
 3. The method of claim 1, further comprisingswitching from the first control strategy to the second control strategyin response to the ETM operating with the first control strategy for atleast a minimum time duration.
 4. The method of claim 1, furthercomprising operating the ETM as the generator in the first controlstrategy before switching from the first control strategy to the secondcontrol strategy.
 5. The method of claim 1, wherein the ETM operates asa starter for the internal combustion engine while controlling the ETMwith the first control strategy.
 6. The method of claim 1, whereinpulse-width modulation (PWM) is used to control the electrical converterconnected between the ETM and the power source, the first controlstrategy including first calculations to determine first widths andfirst timings of pulses delivered to the electrical converter, thesecond control strategy including second calculations different from thefirst calculations to determine second widths and second timings ofpulses delivered to the electrical converter.
 7. The method of claim 1,wherein the first control strategy comprises a vector control, thevector control comprising: controlling a delivery of electric power fromthe power source to the ETM based on a pre-determined torque requestsufficient to cause rotation of a crankshaft of the internal combustionengine.
 8. The method of claim 1, wherein the first control strategycomprises a vector control, the vector control comprising: determining aspeed request sufficient to start the internal combustion engine; andcontrolling a delivery of electric power from the power source to theETM based on the determined speed request.
 9. The method of claim 1,wherein operating the ETM as the generator comprises shunting an outputof the ETM in response to the ETM generating a voltage that exceeds amaximum voltage threshold.
 10. The method of claim 1, wherein operatingwith the second control strategy comprises delivering electric powerfrom the ETM to the accessory at a desired voltage over a range ofrotational speeds of the internal combustion engine, the range ofrotational speeds being greater than the minimum revolution threshold.11. The method of claim 1, wherein the power source is selected from abattery and a capacitance.
 12. The method of claim 1, wherein: theaccessory is the power source; and operating under the second controlstrategy comprises operating the ETM as the generator to charge thepower source.
 13. The method of claim 12, further comprising deliveringelectric power to the ETM using the first control strategy in responseto sensing a command to start the internal combustion engine.
 14. Themethod of claim 13, wherein electric power is delivered using the firstcontrol strategy in response to a voltage of the power source beingequal to or above a first minimum voltage threshold.
 15. The method ofclaim 14, further comprising: terminating the delivery of electric powerin response to the voltage of the power source falling below a secondminimum voltage threshold lower than the first minimum voltagethreshold; and providing a manual start indication in response toterminating the delivery of electric power.
 16. The method of claim 1,further comprising: sensing a command to start the internal combustionengine; and in response to sensing the command to start the internalcombustion engine, providing a manual start indication in response to avoltage of the power source being below a first minimum voltagethreshold.
 17. The method of claim 1, wherein the internal combustionengine comprises: a cylinder; a cylinder head connected to the cylinder;a piston disposed in the cylinder, the cylinder, the cylinder head andthe piston defining a variable volume combustion chamber therebetween;and a crankshaft operatively connected to the piston; wherein the ETM isoperatively connected to the crankshaft.
 18. The method of claim 17,further comprising: delivering fuel in the combustion chamber as thepiston moves toward its top dead center (TDC) position and igniting thefuel in the combustion chamber as the piston moves beyond its TDCposition; wherein delivering the fuel in the combustion chambercomprises injecting the fuel in the combustion chamber.
 19. The methodof claim 1, further comprising determining the rotational speed of theinternal combustion engine.